Spatial light modulator and mirror array device

ABSTRACT

The present invention provides a spatial light modulator, comprising: a pixel array comprises a plurality of pixel units. Each of the pixel units comprises a memory cell. A plurality of word lines and a plurality of plate lines to electrically communicate with the pixel units. A plurality of bit line sets wherein each of the sets includes a pair of bit lines each connected to a memory cell, wherein at least one pair of the memory cells connected to the pair of bit lines are on a same row connected to a same word line.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Non-provisional Application claiming a Prioritydate of Nov. 16, 2007 based on a previously filed ProvisionalApplication 61/003,398 and a Non-provisional patent application Ser. No.11/121,543 filed on May 3, 2005 issued into U.S. Pat. No. 7,268,932. Theapplication Ser. No. 11/121,543 is a Continuation In Part (CIP)Application of three previously filed Applications. These threeApplications are Ser. No. 10/698,620 filed on Nov. 1, 2003, Ser. No.10/699,140 filed on Nov. 1, 2003 now issued into U.S. Pat. No.6,862,127, and Ser. No. 10/699,143 filed on Nov. 1, 2003 now issued intoU.S. Pat. No. 6,903,860 by the Applicant of this Patent Applications.The disclosures made in these Patent Applications are herebyincorporated by reference in this Patent Application.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to systems and methods toconfigure a projection apparatus comprising a spatial light modulator.More particularly this invention relates to systems and methods forimplementing a new and improved spatial light modulator in a projectionapparatus to achieve a higher quality of image display.

2. Description of the Related Art

After the dominance of CRT technology in the display industry for over100 years, Flat Panel Display (FPD) and Projection Display have gainedpopularity because of their space efficiency and larger screen size.Projection displays using micro-display technology are gainingpopularity among consumers because of their high picture quality andlower cost. There are two types of micro-displays used for projectiondisplays in the market. One is micro-LCD (Liquid Crystal Display) andthe other is micro-mirror technology. Because a micro-mirror device usesun-polarized light, it produces better brightness than micro-LCD, whichuses polarized light.

Although significant advances have been made in technologies ofimplementing electromechanical micro-mirror devices as spatial lightmodulators, there are still limitations in their high quality imagesdisplay. Specifically, when display images are digitally controlled,image quality is adversely due to an insufficient number of gray scales.

Electromechanical micro-mirror devices have drawn considerable interestbecause of their application as spatial light modulators (SLMs). Aspatial light modulator requires an array of a relatively large numberof micro-mirror devices. In general, the number of required devicesranges from 60,000 to several million for each SLM. Referring to FIG.1A, an image display system 1 including a screen 2 is disclosed in arelevant U.S. Pat. No. 5,214,420. A light source 10 is used to generatelight beams to project illumination for the display images on thedisplay screen 2. The light 9 projected from the light source is furtherconcentrated and directed toward lens 12 by way of mirror 11. Lenses 12,13 and 14 form a beam columnator operative to columnate the light 9 intoa column of light 8. A spatial light modulator 15 is controlled by acomputer through data transmitted over data cable 18 to selectivelyredirect a portion of the light from path 7 toward lens 5 to display onscreen 2. FIG. 1B shows a SLM 15 that has a surface 16 that includes anarray of switchable reflective elements 17, 27, 37, and 47, each ofthese reflective elements is attached to a hinge 30. When the element 17is in an ON position, a portion of the light from path 7 is reflectedand redirected along path 6 to lens 5 where it is enlarged or spreadalong path 4 to impinge on the display screen 2 to form an illuminatedpixel 3. When the element 17 is in an OFF position, the light isreflected away from the display screen 2 and, hence, pixel 3 is dark.

The on-and-off states of the micromirror control scheme, as thatimplemented in the U.S. Pat. No. 5,214,420 and in most conventionaldisplay systems, impose a limitation on the quality of the display.Specifically, applying the conventional configuration of a controlcircuit limits the gray scale gradations produced in a conventionalsystem (PWM between ON and OFF states), limited by the LSB (leastsignificant bit, or the least pulse width). Due to the ON-OFF statesimplemented in the conventional systems, there is no way of providing ashorter pulse width than the duration represented by the LSB. The leastquantity of light, which determines the gray scale, is the lightreflected during the least pulse width. The limited levels of gray scalelead to a degradation of the display image.

Specifically, FIG. 1C exemplifies, as related disclosures, a circuitdiagram for controlling a micromirror according to U.S. Pat. No.5,285,407. The control circuit includes memory cell 32. Varioustransistors are referred to as “M*” where “*” designates a transistornumber and each transistor is an insulated gate field effect transistor.Transistors M5, and M7 are p-channel transistors; transistors, M6, M8,and M9 are n-channel transistors. The capacitances, C1 and C2, representthe capacitive loads in the memory cell 32. The memory cell 32 includesan access switch transistor M9 and a latch 32 a based on a Static RandomAccess switch Memory (SRAM) design. All access transistors M9 on a Rowline receive a DATA signal from a different Bit-line 31 a. Theparticular memory cell 32 is accessed for writing a bit to the cell byturning on the appropriate row select transistor M9, using the ROWsignal functioning as a Word-line. Latch 32 a consists of twocross-coupled inverters, M5/M6 and M7/M8, which permit two stable statesthat include a state 1 when is Node A high and Node B low, and a state 2when Node A is low and Node B is high.

The control circuit positions the micro-mirrors to be at either an ON oran OFF angular orientation, as that shown in FIG. 1A. The brightness,i.e., the number of gray scales of display for a digitally control imagesystem, is determined by the length of time the micro-mirror stays at anON position. The length of time a micromirror is in an ON position iscontrolled by a multiple bit word. FIG. 1D shows the “binary timeintervals” when controlling micromirrors with a four-bit word. As shownin FIG. 1D, the time durations have relative values of 1, 2, 4, 8, whichin turn define the relative brightness for each of the four bits where“1” is the least significant bit and “8” is the most significant bit.According to the control mechanism as shown, the minimum controllabledifferences between gray scales for showing different levels ofbrightness is a represented by the “least significant bit” thatmaintains the micromirror at an ON position.

For example, assuming n bits of gray scales, one time frame is dividedinto 2^(n)−1 equal time periods. For a 16.7-millisecond frame period andn-bit intensity values, the time period is 16.7/(2^(n)−1) milliseconds.

Having established these times for each pixel of each frame, pixelintensities are quantified such that black is a 0 time period, theintensity level represented by the LSB is 1 time period, and the maximumbrightness is 2^(n)−1 time periods. Each pixel's quantified intensitydetermines its ON-time during a time frame. Thus, during a time frame,each pixel with a quantified value of more than 0 is ON for the numberof time periods that correspond to its intensity. The viewer's eyeintegrates the pixel brightness so that the image appears the same as ifit were generated with analog levels of light.

For controlling deflectable mirror devices, the PWM applies data to beformatted into “bit-planes”, with each bit-plane corresponding to a bitweight of the intensity of light. Thus, if the brightness of each pixelis represented by an n-bit value, each frame of data has then-bit-planes. Then, each bit-plane has a 0 or 1 value for each mirrorelement. According to the PWM control scheme described in the precedingparagraphs, each bit-plane is independently loaded and the mirrorelements are controlled according to bit-plane values corresponding tothe value of each bit during one frame. Specifically, the bit-planeaccording to the LSB of each pixel is displayed for 1 time period.

Meanwhile, higher levels of resolution and higher grades of gray scalesrequired for better quality display images are in demand for projectionapparatuses, especially in recent years due to the increasedavailability of video images, such as that provided by high definitiontelevision (HDTV) broadcasting.

However, in the gray scale control by the pulse width modulation (PWM),as shown in FIG. 1D, the expressible gray scale is limited by the lengthof the time period determined by the LSB. An attempt to add a newcontrol structure to a memory cell of the above described SRAM structurein order to overcome the aforementioned limitation creates anotherproblem, that is, the structure of a complex memory cell, with a largernumber of transistors than, for example, the memory cell of a DRAMstructure, increases the size of the mechanism.

That is, in order to obtain a higher definition display image, a largenumber of mirror elements are required. Each of these mirror elements,comprising an SRAM-structured memory cell, must be reduced in size tofit in the space of a certain mounting size (e.g., a predefined packagesize or chip size). However, the addition of a new control structure toan SRAM-structured memory cell in order to attain a higher level grayscale display image increases the size of the memory cell, therebyinhibiting a higher level display image.

SUMMARY OF THE INVENTION

The present invention aims at providing a technique for enabling both ahigher level of definition and a higher grade of gray scale of aprojection image in a projection technique using a spatial lightmodulator.

A first exemplary embodiment of the present invention provides a spatiallight modulator, comprising: a pixel array comprises a plurality ofpixel units; each of the pixel units further comprises a memory cell; aplurality of word lines and a plurality of plate lines for electricallycommunicating with the pixel units; and a plurality of bit line setswherein each of the sets includes a pair of bit lines each connected toa memory cell, wherein at least one pair of the memory cells connectedto the pair of bit lines are on a same row connected to a same wordline.

A second exemplary embodiment of the present invention provides thespatial light modulator according to the first exemplary embodiment,wherein at least two of the memory cells are connected to the set of bitlines in one of the pixel units.

A third exemplary embodiment of the present invention provides thespatial light modulator according to the first exemplary embodiment,wherein every other of the memory cells on one row in a direction alongthe word line is connected to the bit line and plate line.

A fourth exemplary embodiment of the present invention provides thespatial light modulator according to the first exemplary embodiment,wherein the memory cells connected to the bit line and the plate lineare configured at common relative location in each row in a directionalong the word line of the pixel array.

A fifth exemplary embodiment of the present invention provides thespatial light modulator according to the first exemplary embodiment,further comprising a bit driver for driving the sets of bit lines,wherein the bit driver has a first operation mode and a second operationmode, wherein a combinations of predetermined pieces of data settransmitted to the bit line set are different in the first operationmode and the second operation mode.

A sixth exemplary embodiment of the present invention provides thespatial light modulator according to the fifth exemplary embodiment,wherein the data with a reversed logic state is applied to each bit lineof the bit line set in the first operation mode, and the data with thesame logic state or reversed logic state is applied to each bit line ofthe bit line set in the second operation.

A seventh exemplary embodiment of the present invention provides thespatial light modulator according to the fifth exemplary embodiment,wherein the signal levels of the plate line are changed after the dataof the second operation mode is applied by the bit line driver to thememory cell.

An eighth exemplary embodiment of the present invention provides thespatial light modulator according to the fifth exemplary embodiment,wherein the second operation mode is carried out at least for one timeduring one sub-frame period for image display.

A ninth exemplary embodiment of the present invention provides thespatial light modulator according to the first exemplary embodiment,wherein each of the pixel units further comprises a mirror.

A tenth exemplary embodiment of the present invention provides a spatiallight modulator, comprising: a pixel array comprises a plurality ofpixel units; each of the pixel units comprises a memory cell forretaining data applied for driving the pixel unit; a plurality of wordlines and a plurality of plate lines for electrically communicating withthe pixel units; and a plurality of bit lines for transmitting the datato the memory cell, wherein the memory comprises a transistor and acapacitor, a word line is connected to the gate of the transistor, thefirst plate of the capacitor is connected to a source of the transistorto for connecting to the bit line, the second plate of the capacitor isconnected to the plate line, a plurality of bit line sets wherein eachof the sets includes two of the bit lines, and the plate line isconnected to at least one of two of the memory cells connected to theset of bit lines wherein the memory cell are disposed on one row in adirection along the word line of the pixel array.

An eleventh exemplary embodiment of the present invention provides thespatial light modulator according to the first or tenth exemplaryembodiment, wherein each of the pixel units comprises a micromirror andan ON electrode and an OFF electrode to control the micromirror todeflect to a range of tilt angles, the memory cells are electricallyconnected corresponding to an ON electrode and an OFF electrode, the bitline is transmits a data signal for storing in the memory cell, the wordline controls the transistor in each of the memory cells for controllingan operation of writing the data signal to the memory cell, and theplate line transmits another data signal to the memory cell.

An twelfth exemplary embodiment of the present invention provides thespatial light modulator according to the first or tenth exemplaryembodiment, wherein each of the pixel units comprises a micromirror, andan ON electrode and an OFF electrode to control the micromirror todeflect within a range of tilt angles, the memory cells are electricallyconnected correspondingly to an ON electrode and an OFF electrode, thebit line is transmits a data signal for storing in the memory cell, theword line controls the transistor in each of the memory cells forcontrolling an operation of writing the data signal to the memory cell,and the plate line applies another data signal to the memory cell.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is described in detail below with reference to thefollowing Figures.

FIG. 1A illustrates the basic principle of a projection display using amicromirror device.

FIG. 1B illustrates the basic principle of a micromirror device used forprojection display.

FIG. 1C shows an exemplary driving circuit of a related art.

FIG. 1D shows the scheme of Binary Pulse Width Modulation (Binary PWM)of conventional digital micromirrors for generating grayscale.

FIG. 2 is a functional block diagram for illustrating the configurationof a display system according to a preferred embodiment of the presentinvention.

FIG. 3 is a block diagram illustrating the configuration of a spatiallight modulator constituting a display system according to a preferredembodiment of the present invention.

FIG. 4 is a cross-sectional outline diagram of one mirror element on theline II-II of the spatial light modulator shown in FIG. 5.

FIG. 5 is a diagonal view diagram showing a part of the configuration ofa spatial light modulator constituting a display system according to apreferred embodiment of the present invention.

FIG. 6 is a chart illustrating a mirror control profile used in adisplay system according to a preferred embodiment of the presentinvention.

FIG. 7A is a cross-sectional diagram showing the ON state of amicromirror.

FIG. 7B is a chart showing the quantity of light projected in the ONstate of a micromirror.

FIG. 7C is a cross-sectional diagram showing the OFF state of amicromirror.

FIG. 7D is a chart showing the quantity of light projected in the OFFstate of a micromirror.

FIG. 7E is a cross-sectional diagram showing the oscillation state of amicromirror.

FIG. 7F is a chart showing the quantity of light projected in theoscillation state of a micromirror.

FIG. 8A is a cross-sectional diagram illustrating the specificconfiguration of a pixel unit in a display system according to apreferred embodiment of the present invention.

FIG. 8B is a plain view diagram of the surface of the pixel unit of FIG.8A.

FIG. 8C is a plain view diagram of FIG. 8A with the mirror removed fromthe pixel unit.

FIG. 8D is a cross-sectional diagram of the mirror element shown in FIG.8A deflected in an ON state.

FIG. 8E is a cross-sectional diagram of the mirror element shown in FIG.8A deflected in an OFF state.

FIG. 9A is a conceptual diagram illustrating the action of a pixel unitof the configuration shown in FIGS. 8A through 8E.

FIG. 9B is a conceptual diagram illustrating the action of a pixel unitof the configuration shown in FIGS. 8A through 8E.

FIG. 9C is a conceptual diagram illustrating the action of a pixel unitof the configuration shown in FIGS. 8A through 8E.

FIG. 9D is a conceptual diagram illustrating the action of a pixel unitof the configuration shown in FIGS. 8A through 8E.

FIG. 10A is a conceptual diagram illustrating an example of aconfiguration of a pixel unit comprised in a display system according toa preferred embodiment of the present invention.

FIG. 10B is a conceptual diagram illustrating an example of amodification of a pixel unit comprised in a display system according toa preferred embodiment of the present invention.

FIG. 10C is a plain view diagram illustrating the layout of a capacitorused in a possible modification of a pixel unit comprised in a displaysystem according to a preferred embodiment of the present invention.

FIG. 10D is a conceptual diagram illustrating another modification of apixel unit comprised in a display system according to a preferredembodiment of the present invention.

FIG. 10E is a conceptual diagram illustrating a possible modification ofa pixel array comprised in a display system according to a preferredembodiment of the present invention.

FIG. 11A is a conceptual diagram illustrating the action of a pixel unitcomprised in a display system according to a preferred embodiment of thepresent invention.

FIG. 11B is a conceptual diagram illustrating the action of a pixel unitcomprised in a display system according to a preferred embodiment of thepresent invention.

FIG. 11C is a conceptual diagram illustrating the action of a pixel unitcomprised in a display system according to a preferred embodiment of thepresent invention.

FIG. 11D is a conceptual diagram showing in greater detail theequalization circuit of FIG. 11B.

FIG. 11E is a conceptual diagram showing in greater detail theequalization circuit of FIG. 11C.

FIG. 12A is a conceptual diagram illustrating the placement of theperipheral circuit of a pixel array comprised in a display systemaccording to a preferred embodiment of the present invention.

FIG. 12B is a conceptual diagram illustrating the internal configurationof a plate line driver (PL Driver) shown in FIG. 12A;

FIG. 12C is a conceptual diagram illustrating the internal configurationof a plate line address decoder (PL Address Decoder-a) shown in FIG.12A.

FIG. 12D is a conceptual diagram showing a possible modificationconfigured by adding a function to the plate line address decoder (PLAddress Decoder-a) shown in FIG. 12C.

FIG. 12E is a diagram illustrating the internal configuration of a bitline driver unit (Bitline Driver) shown in FIG. 12A.

FIG. 12F is a truth table for regulating the operation of the bit linedriver unit (Bitline Driver) shown in FIG. 12E.

FIG. 13 is a timing chart illustrating the operation of a pixel array ofthe configuration shown in FIG. 10A.

FIG. 14 is a timing chart of the address decoder for the ROW lines shownin FIG. 12A.

FIG. 15 is a conceptual diagram showing another possible modification ofthe pixel unit shown in FIG. 10A.

FIG. 15A is a cross-sectional diagram of a pixel unit in an ON statecomprising two electrodes, i.e., an ON electrode and a second ONelectrode, on the ON side shown in FIG. 15.

FIG. 15B is a cross-sectional diagram of a pixel unit in an OFF statecomprising two electrodes, i.e., an ON electrode and a second ONelectrode, on the ON side shown in FIG. 15.

FIG. 15C is a plain view diagram showing a possible layout of the secondON electrode that is added to the pixel unit shown in FIG. 15.

FIG. 15D is a plain view diagram showing another possible layout of thesecond ON electrode that is added to the pixel unit shown in FIG. 15.

FIG. 15E is a plain view diagram showing another possible layout of thesecond ON electrode that is added to the pixel unit shown in FIG. 15.

FIG. 15F is a plain view diagram showing another possible layout of thesecond ON electrode that is added to the pixel unit shown in FIG. 15.

FIG. 15G is a conceptual diagram showing a modification of the memorycell on the ON side of the pixel unit shown in FIG. 15.

FIG. 15H is a conceptual diagram showing a modification of theconnection between the memory cell on the ON side, a word line, and aplate line at the pixel unit shown in FIG. 15.

FIG. 16 is a timing chart showing the action of the pixel unit shown inFIG. 15.

FIG. 17A is a chart illustrating the setup of a mirror control profile.

FIG. 17B is a chart illustrating the setup of a mirror control profile.

FIG. 17C is a chart illustrating the setup of a mirror control profile.

FIG. 17D is a chart illustrating the setup of a mirror control profile.

FIG. 17E is a chart illustrating the setup of a mirror control profile.

FIG. 17F is a chart illustrating the setup of a mirror control profile.

FIG. 17G is a chart illustrating the setup of a mirror control profile.

FIG. 18 is a conceptual diagram showing another possible modification ofthe pixel unit shown in FIG. 10A.

FIG. 19 is a timing chart showing the action of another possiblemodification of the pixel unit shown in FIG. 18.

FIG. 20 is a conceptual diagram illustrating the layout of a peripheralcircuit performing the action of the pixel unit shown in FIG. 18.

FIG. 21 is a conceptual diagram showing another possible modification ofthe pixel unit shown in FIG. 10A.

FIG. 22A is a conceptual diagram showing a possible modification of theplacement of the peripheral circuit for a pixel array according to apreferred embodiment of the present invention.

FIG. 22B is a conceptual diagram showing a possible modification of theplacement of the peripheral circuit for a pixel array according to apreferred embodiment of the present invention.

FIG. 22C is a conceptual diagram showing a possible modification of theplacement of the peripheral circuit for a pixel array according to apreferred embodiment of the present invention.

FIG. 22D is a conceptual diagram showing a possible modification of theconfiguration of placing the peripheral circuit for a pixel arrayaccording to a preferred embodiment of the present invention.

FIG. 23A is a cross-sectional diagram for showing an exemplarymodification of the configuration of a pixel unit (i.e., a mirrorelement) comprising a mirror implemented with a cantilever structureaccording to a preferred embodiment of the present invention.

FIG. 23B is a cross sectional schematic diagram showing an exemplaryconfiguration of the drive circuit shown in FIG. 23A.

FIG. 24 is a circuit diagram illustrating in detail a part of the layoutof the pixel unit comprising a mirror (shown in FIG. 23A) that isstructured as a cantilever.

FIG. 25 is a timing chart illustrating the action of a pixel unit (i.e.,a mirror element) comprising a mirror (shown in FIG. 23A) that isstructured as a cantilever.

FIG. 26A is a plain view diagram illustrating the packaging structure ofa package accommodating a spatial light modulator according to apreferred embodiment of the present invention.

FIG. 26B is a cross-sectional diagram of FIG. 26A.

FIG. 27 is a conceptual diagram showing the configuration of aprojection apparatus according to a preferred embodiment of the presentinvention.

FIG. 28 is a block diagram illustrating the configuration of a controlunit comprised in the projection apparatus shown in FIG. 27.

FIG. 29 is a conceptual diagram showing another possible modification ofa multi-panel projection apparatus according to a preferred embodimentof the present invention.

FIG. 30 is a block diagram showing a possible configuration of thecontrol unit of a multi-panel projection apparatus according to apreferred embodiment of the present invention.

FIG. 31 is a conceptual diagram showing a possible modification of amulti-panel projection apparatus according to another preferredembodiment of the present invention.

FIG. 32 is a block diagram showing a possible configuration of a controlunit comprised in the projection apparatus shown in FIG. 31.

FIG. 33 is a chart showing the waveform of a control signal of theprojection apparatus shown in FIG. 31.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following is a description, in detail, of the preferred embodimentof the present invention with reference to the accompanying drawings.

FIG. 2 is a conceptual diagram for illustrating the configuration of adisplay system according to a preferred embodiment of the presentinvention. FIG. 3 is a block diagram illustrating the configuration of aspatial light modulator constituting a display system according to apreferred embodiment of the present invention. FIG. 4 is a crosssectional view showing a schematic diagram for illustrating theconfiguration of a pixel unit 211 implemented in a spatial lightmodulator shown according to the present embodiment.

The following description first describes a configuration of aprojection apparatus 100 according to the present embodiment, whichserves as a premise for the individual embodiments, whose descriptionsare also included.

The projection apparatus 100 according to the present embodimentcomprises a spatial light modulator 200, a control apparatus 300, alight source 510, and a projection optical system 520.

FIG. 5 is a diagram for showing a perspective view along a diagonaldirection of a spatial light modulator in which multiple mirror elements(i.e., pixel units) for modulating the reflecting direction of incidentlight by deflecting mirrors are formed as a two-dimensional array on adevice substrate.

As shown in FIG. 5, the spatial light modulator 200 is configured withthe pixel units 211 arranged as a two-dimensional array on a substrate214. Each pixel unit comprises an address electrode (not shown in thedrawing here), an elastic hinge (not shown in the drawing here), and amirror 212 supported by the elastic hinge. According to theconfiguration shown in FIG. 5, pixel units 211 having square mirrors 212arranged in a two-dimensional array on substrate 214. Voltages appliedto an address electrode formed on the substrate 214 control the mirror212 in each pixel unit 211 to move to different deflection angles.

Meanwhile, in consideration of the number of pixels required by a superhigh definition television, the pitch, i.e., the interval betweenadjacent mirrors 212, is set between 4 μm and 14 μm, or, preferably,between 5 μm and 10 μm, to achieve the resolution of a full HD TV, e.g.,2048 by 4096, or a non-full TD TV, and of the size of mirror devices.More specifically, the pitch is defined as the distance between thedeflection axes of adjacent mirrors 212. In an exemplary embodiment, thearea of a mirror 212 may be between 16 μm² and 196 μm², or, preferably,between 25 μm² and 100 μm². Note that the shape mirror 212 or the pitchbetween the mirrors 212 may be flexibly adjusted according to specificrequirements of display resolution.

The drawing also shows a dotted line as a deflection axis 212 a of themirror 212. Specifically, when the light emitted from a light source 510is a coherent light, the angle of incident to mirror 212 is configuredalong a orthogonal or diagonal direction relative to deflection axis 212a. The light source 510 emits a coherent light when the light source isimplemented as a laser light source.

The following description further explains the control processes and theoperation of the pixel unit 211 with reference to the cross-sectionaldiagram across the line II-II over a pixel unit of the spatial lightmodulator 200 shown in FIG. 5. Specifically, FIG. 4 is a cross-sectionaloutline diagram for showing a cross-section of one mirror element of thespatial light modulator on the line II-II in FIG. 5.

As illustrated in FIGS. 3 and 4, a spatial light modulator 200 accordingto the present embodiment comprises a pixel array 210, a bit line driverpart 220, and a word line driver unit 230.

In pixel array 210, multiple pixel units 211 are arrayed on a grid ateach of the positions where bit lines 221 extending vertically from thebit line driver part 220 cross word lines 231 extending horizontallyfrom the word line driver unit 230.

As illustrated in FIG. 4, each pixel unit 211 comprises a mirror 212that freely tilts and is supported on the substrate 214 by a hinge 213.

An OFF electrode 215 and an OFF stopper 215 a are placed symmetricallyacross hinge 213 that comprises a hinge electrode 213 a on the substrate214, and likewise an ON electrode 216 and an ON stopper 216 a are placedthereon.

A predetermined voltage applied to the OFF electrode 215 draws mirror212 with a Coulomb force to tilt to an angular position abutting the OFFstopper 215 a. The mirror 212 thus reflects the incident light 511 tothe light path along an OFF direction away from the optical axis of aprojection optical system 130.

A predetermined voltage applied to the ON electrode 216 draws the mirror212 with a Coulomb force to tilt to an angular position abutting the ONstopper 216 a. The mirror 212 reflects the incident light 311 to thelight path along an ON direction coincident with the optical axis of theprojection optical system 130.

FIG. 4 shows an OFF capacitor 215 b is connected to the OFF electrode215 and to the bit line 221-1 by way of a gate transistor 215 c that isimplemented as a field effect transistor (FET). An ON capacitor 216 b isconnected to the ON electrode 216, and to the bit line 221-2 by way of agate transistor 216 c that is implemented as a field effect transistor(FET).

The signal on the wordline 231 controls the turning ON and OFF of thegate transistor 215 c.

Specifically, a select signal on a word line 231 simultaneously selectsall the pixel units 211 connected to the horizontal word line 231. Thesignals on the bitlines 221-1 and 221-2 control the charging anddischarging of the OFF capacitor 215 b and ON capacitor 216 b.Therefore, the micromirror 212 in each pixel unit 211 along a horizontalrow is controlled to turn ON and OFF.

A memory cell M1 configured with a DRAM structure includes an OFFcapacitor 215 b and gate transistor 215 c on the side of the OFFelectrode 215. Likewise, the memory cell M2 also configured with a DRAMstructure includes an ON capacitor 216 b and gate transistor 216 c onthe side of the ON electrode 216. With this configuration, the tiltingoperation of the mirror 212 is controlled in accordance with thepresence and absence data written to the respective memory cells of theOFF electrode 215 and ON electrode 216.

The light source 510 emits an incident light 511 to illuminate thespatial light modulator 200. The individual micromirrors 212 thenreflects the incident light 511 as the reflection light 512. Reflectionlight 512 on the light path passes through a projection optical system520 and is projected onto a screen (not shown in a drawing herein) orthe like, as projection light 513.

The descriptions below explain the operation of a control apparatus 300according to the present embodiment. The control apparatus controls thespatial light modulator 200 to operate in the ON/OFF states (i.e., anON/OFF modulation) and oscillation state (i.e., an oscillationmodulation) of mirror 212 of the spatial light modulator 200 to achievea higher level of gray scales by operating with an intermediate grayscale.

A non-binary block 320 generates non-binary data 430 used forcontrolling mirror 212 by converting, into non-binary data, a binaryvideo image signal 400 that is externally input binary data. In thisevent, the LSB is different for the period of ON/OFF states of themirror 212 and the period of intermediate oscillation state.

A timing control unit 330 generates a drive timing 420 for thenon-binary block 320, a PWM drive timing 440, and an OSC drive timing441 for the mirror 212 on the basis of an input synchronous signal 410(Sync).

As illustrated in FIG. 6, the present embodiment is configured such thata desired number of bits of the upper bits 401 of the binary video imagesignal 400 is assigned to the ON/OFF control for the mirror and theremaining lower number of bits 402 is assigned to the oscillationcontrol. The control is such that the ON/OFF (positioning) state iscontrolled by the PWM drive timing 440 from the timing control unit 330and the non-binary data 430, while the oscillation state is controlledby the PWM drive timing 440 and OSC drive timing 441 from the timingcontrol unit 330 and the non-binary data 430.

The following is a description of the basic control of a micromirror 212of a spatial light modulator 200 according to the present embodiment.

Note that “Va (1, 0)” indicates an application of a predeterminedvoltage Va to the OFF electrode 215 and no application of voltage to theON electrode 216 in the following description.

Also, “Va (0, 1)” indicates no application of voltage to the OFFelectrode 215 and an application of a voltage Va to the ON electrode216.

Also, “Va (1, 1) indicates the application of a voltage Va to both theOFF electrode 215 and ON electrode 216.

FIGS. 7A, 7B, 7C, 7D, 7E and 7F show the configuration of a pixel unit211 comprising a mirror 212, a hinge 213, OFF electrode 215, and ONelectrode 216, and a basic example of how a mirror 212 is controlledunder an ON/OFF state and under an oscillating state.

FIG. 7A shows the mirror 212 having been tilted from the neutral stateby being attracted by the ON electrode 216, thus tilting to an ON state,as a result of applying a predetermined voltage (i.e., Va (0, 1)) toonly the ON electrode 216. In the ON state of micromirror 212,reflection light 512 by way of mirror 212 is captured by projectionoptical system 520 and projected as projection light 513. FIG. 7B showsthe quantity of light projected in the ON state.

FIG. 7C shows the mirror 212 having been tilted from the neutral stateby being attracted by the OFF electrode 215, thus tilting to an OFFstate, as a result of applying a predetermined voltage (i.e., Va (1, 0))to only the OFF electrode 215. In the OFF state of micromirror 212,reflection light 512 is deflected away from projection optical system520, and therefore does not transmit light along the optical path of theprojection light 513. The right side of FIG. 7B shows the quantity oflight projected in the OFF state. FIG. 7D shows the quantity of lightprojected in the OFF state.

FIG. 7E illustrates mirror 212 performing a free oscillation in themaximum amplitude of A0 between a tilted position (i.e., a Full ON),contacting with the ON electrode 216, and another tilted position (i.e.,a Full OFF), contacting with the OFF electrode 215 (at Va (0, 0)).

Incident light 511 is projected onto the micromirror 212 at a prescribedangle, and the quantity of light resulting from incident light 511reflecting in the ON direction. A portion of the quantity of light (i.e.the quantity of light of the reflection light 512) reflecting in adirection that is between the ON direction and OFF direction areincident to projection optical system 520 so as to be projected as thebrightness of the image (i.e., the projection light 513). FIG. 7F showsthe quantity of light projected in an oscillation state.

That is, in the ON state of mirror 212 shown in FIG. 7A, the flux oflight of reflection light 512 proceeds to the ON direction so as to becaptured almost entirely by projection optical system 520 and projectedas projection light 513.

In the OFF state of mirror 212, shown in FIG. 7C, reflection light 512proceeds to an OFF direction shifted from projection optical system 520,and thus a light projected as projection light 513 does not exist.

In the oscillating state of mirror 212, shown in FIG. 7E, a portion ofthe light flux of reflection light 512, diffraction light, diffusionlight, and the like are captured by projection optical system 520 andprojected as projection light 513.

Note that the examples shown in FIGS. 7A, 7B, 7C, 7D, 7E and 7Fdescribed above have been described for in the case of applying thevoltage Va represented by a binary value of “0” or “1” to OFF electrode215 and ON electrode 216. However, a more precise control of the tiltingangle of mirror 212 is possible by increasing the steps of Coulomb forcegenerated between mirror 212 and OFF electrode 215 or ON electrode 216by increasing the step of the voltage value Va to multiple values.

Also note that the examples shown in FIGS. 7A, 7B, 7C, 7D, 7E and 7Fdescribed above presume that mirror 212 (i.e., the hinge electrode 213a) is set at the ground potential. However, a more precise control ofthe tilting angle of the mirror 212 is possible by applying an offsetvoltage thereto.

The present embodiment is configured to apply the voltages, i.e., Va (0,1), Va (1, 0) and Va (0, 0), at the appropriate times during the tiltingof the mirror 212 between the ON and OFF states as described below so asto generate a free oscillation in an amplitude that is smaller than themaximum amplitude between the ON and OFF states, thereby producing amore refined gray scale.

The following describes a method for displaying a video image using theprojection apparatus according to the present embodiment.

Non-binary data 430, a PWM drive timing 440, and an OSC drive timing 441are generated when a binary video image signal 400 and a synchronoussignal 410 are input to a control apparatus 300.

Non-binary block 320 and timing control unit 330 calculate the period oftime for controlling mirror 212 under an ON state. That is, theycalculate the time for controlling the mirror 212 under an oscillationstate, or the number of times for oscillating the mirror 212 for eachmirror 212 of spatial light modulator 200, which displays the pixels ofa video image in accordance with binary video image signal 400 and drivetiming 420. Drive timing 420 is generated by timing control unit 330from synchronous signal 410, and it generates non-binary data 430, a PWMdrive timing 440, and an OSC drive timing 441.

Here, non-binary block 320 and timing control unit 330, that arecomprised in control apparatus 300, use the ratio of the quantity oflight of a projection light 513, obtained by oscillating a predeterminedmirror 212 in an oscillation time T, to the quantity of light of aprojection light 513, obtained by controlling mirror 212 under an ONstate during the oscillation time T. This ratio is used to calculate theperiod of time for controlling mirror 212 under an ON state, the periodof time for controlling the mirror 212 under the oscillation state, orthe number of oscillations of mirror 212.

Non-binary data 430, PWM drive timing 440, and OSC drive timing 441 aregenerated on the basis of the calculated value of the time or the numberof oscillations used to perform the ON/OFF control and oscillationcontrol for each of the mirrors 212 constituting one frame of videoimage.

FIG. 8A is a cross-sectional diagram illustrating the specificconfiguration of a pixel unit 211 in the above described spatial lightmodulator 200.

The mirror element shown in FIG. 8A comprises wirings 1) 906 a, 906 b,and 906 c of a drive circuit used for driving and controlling a mirror913, 2) first Vias 907 a, 907 b, 907 c, 907 d, 907 d, and 907 e, all ofwhich are connected to the wirings 906 a, 906 b, and 906 c of the drivecircuit, and 3) a first insulation layer 902, which is on a substrate901. Wiring 906 a on the left side is implemented with two first Vias907 a and 907 e, and with first insulation layer 902 separating the twoVias. Likewise, wiring 906 b on the right side is also implemented withtwo first Vias 907 b and 907 d, and with first insulation layer 902separating the two Vias. Wiring 906 c in the center is implemented withonly one first via 907 a. In summary, the present embodiment isimplemented with five first Vias each has an insulation layer.

The present embodiment is also implemented with the wirings on the leftand right sides with two first Vias. The number of first Vias may bedifferent between the left and right sides. The number of first Vias mayalso be greater or fewer than in the present embodiment.

Furthermore, on the first Vias 907 a, 907 b, 907 c, 907 d, 907 d, and907 e are formed second Vias 915 a, 915 b, and 915 c and surfaceelectrodes 908 a and 908 b, all of which are formed on the right andleft sides the second Vias, respectively.

The second via 915 a is formed on the first via 907 a, which has beenformed on wiring 906 c at the center. The second Vias 915 b and 915 care formed on first Vias 907 b and 907 c, respectively, both of whichare formed on the wirings 906 a and 906 b on the left and right sides,respectively. Surface electrodes 908 a and 908 b are formed on firstVias 907 d and 907 e, respectively, whereas second Vias 915 a, 915 b, or915 c is not formed on wirings 906 a and 906 b.

Furthermore, a first protective layer 903 is laid on the firstinsulation layer 902, and a second protective layer 904 is laid on thefirst protective layer 903.

Substrate 901 is preferably a silicon substrate.

Wirings 906 a, 906 b, and 906 c of the drive circuit are preferablyaluminum wirings.

First Vias 907 a, 907 b, 907 c, 907 d, 907 d, and 907 e and second Vias915 a, 915 b, and 915 c are preferably made of a metallic materialcontaining tungsten and/or copper.

Surface electrodes 908 a and 908 b may be made of a material similar tothat of first Vias 907 a, 907 b, 907 c, 907 d, 907 d, and 907 e andsecond Vias 915 a, 915 b, and 915 c (e.g., tungsten), or of a materialwith high electrical conductivity, such as aluminum. The form of thesurface electrodes 908 a and 908 b is arbitrary. FIG. 8 illustrates anexample of placing the surface electrodes 908 a and 908 b on first Vias907 d and 907 e, respectively. They may alternatively be placed directlyon wirings 906 a and 906 b.

First insulation layer 902, first protective layer 903, and secondprotective layer 904 are preferably layers containing silicon such assilicon carbide (SiC), amorphous silicon, or silicon dioxide (SiO₂).

If aluminum is used for surface electrodes 908 a and 908 b, a directcontact between the amorphous silicon and aluminum electrode corrodesthe aluminum surface electrodes 908 a and 908 b, and therefore a siliconcarbide (SiC) layer between the amorphous silicon and aluminum surfaceelectrodes 908 a and 908 b is recommended. Alternatively, an electrodemay be formed by mixing aluminum with an impurity, such as silicon;alternatively, a barrier layer may be provided by using a material otherthan a SiC layer. Such a barrier layer may comprise two layers or more.

For example, first insulation layer 902 of FIG. 8A is a layer made ofsilicon carbide (SiC). First insulation layer 902 may be made of anothermaterial such as titanium nitride (TiN), or the like, which takes intoconsideration the etching of a dispensable layer with hydrogen fluoride(HF), which is employed for producing a mirror element; this also takesinto consideration the stiction of between a mirror element andelectrode 909 a or 909 b when the former deflects and abuts onto thelatter.

The mirror element, according to the present embodiment, is equipselectrodes 909 a, 909 b, and 914 so as to a secure electrical connectionto second Vias 915 a, 915 b, and 915 c, respectively.

Electrodes 909 a, 909 b, and 914 may preferably use a high electricallyconductive material such as aluminum.

Electrode 914, shown in FIG. 8A, (constituting a hinge electrode later)is an electrode equipped with an elastic hinge 911 and is configured tobe the same height as electrodes 909 a and 909 b on the left and right.Configuring individual electrodes 909 a, 909 b, and 914 to be the sameheight as the center, left, and right makes it possible to form thethree electrodes 909 a, 909 b and 914 in the same production process.Furthermore, a barrier layer 910 made of tantrum, titanium, or such isplaced on electrode 914 at the center. Barrier layer 910 may comprisetwo layers or more.

Furthermore, an appropriate modification of the height of the electrodeat the center makes it possible to determine the height for placing anelastic hinge 911 at the center described below. The height of theplacement of elastic hinge 911 may be determined by adjusting the heightof barrier layer 910.

Elastic hinge 911 is placed on electrode 914 at the center, on whichbarrier layer 910 has been laid, so as to be connected to barrier layer910.

Elastic hinge 911 is made of a material such as amorphous silicon. Thethickness of elastic hinge 911 (in the left and right direction of thedrawing of FIG. 8A) is preferably between approximately 150 and 400angstroms.

Multiple elastic hinges may be provided for one mirror and the mirrormay be supported by such elastic hinges that are reduced in width. Forexample, two elastic hinges narrower than the conventional configurationmay be used one mirror at either end of the mirror.

Elastic hinge 911 is preferably applied with In-Situ doping (such asarsenic and phosphorus), an ion implanting, a diffusion of metallicsilicide, such as nickel silicide (NiSi), titanium silicide (TiSi), soas to possess electric conductivity.

Furthermore, the mirror element according to the present embodimentprovides a second insulation layer 905 on the surface of the substratewhere electrodes 909 a, 909 b, and 914 have been placed.

Second insulation layer 905 is preferably a layer containing silicon,such as silicon carbide (SiC), amorphous silicon, or silicon dioxide(SiO₂). This layer is provided to prevent corrosion by hydrogen fluoride(HF) if the electrodes 908 a, 908 b, 909 a, 909 b, and 914 are made ofaluminum as described above.

The upper surface of elastic hinge 911 may be provided with a joinderlayer, which can be configured to be the same form and size as mirror913 described below. The present embodiment is configured so that thejoinder layer is the smallest possible size. Such a configuration makesit possible to prevent mirror 913 from being deformed or warped by thedifference in thermal expansion coefficients between mirror 913 and thejoinder layer.

Furthermore, a metallic layer 912 is laid on the joinder layer ofelastic hinge 911 in order to provide electric conductivity betweenelastic hinge 911 and mirror 913, while eliminating a variation inheights between individual mirror elements.

Metallic layer 912 is made of a material containing tungsten ortitanium; a material containing another metal may also be used.

If mirror 913 is made of aluminum and elastic hinge 911 is made with asilicon material, then a barrier layer (not shown in a drawing herein)may further be laid on and under metallic layer 912 in order to preventmirror 913 from touching elastic hinge 911. Such a barrier layer maycomprise two layers or more.

The barrier layer is made of a material containing tantrum, or titanium,et cetera.

Furthermore, the mirror element according to the present embodiment isconfigured by placing a mirror 913 on metallic layer 912 of elastichinge 911.

Mirror 913 is preferably made of a material with high lightreflectivity, such as aluminum.

Mirror 913 is also preferably has an approximately square shape, withone side measuring between 4.5 and 11 μm. The gap between individualmirrors 913 is preferably between 0.15 and 0.55 μm. The aperture ratioof each individual mirror element is preferably about 90%.

Such is the configuration of the mirror element according to the presentembodiment shown in FIG. 8A.

FIG. 8B is a plain view diagram of the surface of the substrate of themirror device according to the present embodiment.

Note that surface electrodes 909 a and 909 b on the left and right, andthe hinge electrode 914, at the center, which are formed on mirror 913and the second Vias 915 a, 915 b, and 915 c are delineated by the dottedlines. Also, the deflection axis of mirror 913 is indicated by chainlines.

As shown in FIG. 8B, second Vias 915 a, 915 b, and 915 c for electricconduction to electrodes 909 a, 909 b, and 914 are placed underelectrodes 909 a, 909 b, and 914. Surface electrodes 908 a and 908 b,placed so as to increase a Coulomb force for deflecting the mirror 913,are placed under the mirror 913.

FIG. 8C is a plain view diagram with mirror 913 of the mirror element,according to the present embodiment, is removed. The position of mirror913 is indicated by dotted lines.

As shown in FIG. 8C, the respective apexes of electrodes 909 a and 909 bat both end of mirror 913 are formed as protrusions. This design ensuresthat the deflection angle of mirror 913 is at a prescribed angle as aresult of mirror 913 hitting the protrusions of electrodes 909 a and 909b when mirror 913 is deflected.

Note than the tips of electrodes 909 a and 909 b are preferably designedso as to make the deflection angle of mirror 913 between 12 and 14degrees. Such a deflection angle of mirror 913 is preferably designed incompliance to the design of the light source and optical system of aprojection apparatus. Furthermore, the length of elastic hinge 911 ofeach mirror element is preferably no larger than 2 μm, and mirror 913 ispreferably an approximate square, with the length of one side being 10μm or smaller.

The surface of the substrate is formed with the electrodes 909 a and 909b and hinge electrode 914 such that the substrate has convex and concavesurfaces.

FIG. 8D is a cross-sectional diagram the mirror element shown in FIG. 8Adeflected in an ON state.

The present embodiment presumes a configuration in which the lightemitted from a light source is an ON light when mirror 913, shown inFIG. 8A, is deflected to the right side, while the light emitted from alight source is an OFF light when the mirror 913 is deflected to theleft side.

When a voltage is not applied to individual surface electrodes 908 a or908 b on the left and right, or to the individual surface electrodes 909a or 909 b, the elastic hinge 911 is not deformed and the mirror 913 istherefore maintained in a horizontal position.

When a voltage to surface electrode 909 b on the right side and tosurface electrode 908 a on the right side is applied, a Coulomb forcedetermined by the following expression is generated:

[top surface area size of electrode]*[voltage applied to electrode]*[thesecond power of the distance between aluminum and mirror].

This Coulomb force is generated between the right surface electrode 909b and mirror 913 and between the right surface electrode 908 a andmirror 913. Mirror 913 is deflected by the total Coulomb force generatedbetween the right surface electrode 909 b and mirror 913 and between theright side surface electrode 908 a and mirror 913.

In this event, the distance between mirror 913 and right surfaceelectrode 908 a is longer than that between mirror 913 and right surfaceelectrode 909 b, and the area of right surface electrode 908 a issmaller than that of the right surface electrode 909 b. Therefore, thegenerated Coulomb force is also smaller than that generated between theright surface electrode 909 b and mirror 913.

Furthermore, when mirror 913 is attracted to right surface electrode 908a as the mirror is deflected as a result, mirror 913 is deflected to anangle between 12 and 14 degrees, and there is a strong reactive force ofthe elastic hinge due to its resilience. The Coulomb force attracts thetip of mirror 913 to the right surface electrode 908 a placed on thesubstrate surface so that mirror 913 can be attracted by a smallerCoulomb force due to the type of movement characteristic of a rigidbody. As a result, the right surface electrode 908 a is capable ofretaining the deflection of mirror 913 in a state for a low voltage tobe applied thereto.

When mirror 913 is deflected to the right side, the surface electrode908 b on the other side (that is, the left side) and the left sidesurface electrode 909 a are put in the same potential and are grounded.

FIG. 8E is a cross-sectional diagram of the mirror element shown in FIG.8A deflected to an OFF state.

In FIG. 8E, the application of a voltage to left side surface electrode909 a and left side surface electrode 908 b makes it possible to deflectmirror 913 to the left side, like to the process described for FIG. 8D.

The principles in operation and the action of the Coulomb force in thiscase are similar to those noted for FIG. 8D and therefore furtherdescriptions are not provided here.

Incidentally, if the forms of mirror 913 and elastic hinge 911 arechanged between the right and left sides of the mirror element, and ifthe resilience of elastic hinge 911 is different for the right and leftsides of the mirror element, and if the deflection control for mirror913 is different for the right and left sides of the mirror element,then the area, height, and placement of the respective surfaceelectrodes 908 a and 908 b, or the respective surface electrodes 909 a,909 b, and 914, on the right and left sides of the mirror element may bechanged so as to apply the appropriate voltage to thereby control thedeflection of mirror 913.

Furthermore, an alternative control may also be performed so thatvoltages are applied in multiple steps to the respective surfaceelectrodes 908 a and 908 b and respective surface electrodes 909 a and909 b on the right and left sides of the mirror element.

Furthermore, the circuits and voltages for driving surface electrode 908a (or 908 b) and surface electrode 909 a (or 909 b) on either one sideof surface electrode 908 a (and surface electrode 909 b) on the rightside of the mirror element and the surface electrode 908 b (and surfaceelectrode 909 a) on the left side of the mirror element may beappropriately changed. In other words, surface electrodes 908 a and 909b are driven together, or surface electrodes 908 b and 909 a are driventogether.

Furthermore, both or either one of surface electrode 908 a (or 908 b)and 909 a (or 909 b) of surface electrodes 908 a and 909 b on the rightside of the mirror element or surface electrode 908 b and electrode 909a on the left side of the mirror element may protrude from the surfaceof the substrate.

Furthermore, both or either one of surface electrode 908 a (or 908 b)and electrode 909 a (or 909 b) of surface electrodes 908 a and 909 b onthe right side of the mirror element or surface electrode 908 b andelectrode 909 a on the left side of the mirror element may be placed onthe surface of the substrate.

As such, mirror 913 of the mirror element according to the presentembodiment is deflected, and thus the reflecting direction of theillumination light can appropriately be changed.

The following is a description of the benefits of placing surfaceelectrode 909 b and surface electrode 909 a on the ON side apart fromeach other in the present embodiment, with reference to FIGS. 9A, 9B,9C, and 9D.

FIG. 9A is a conceptual diagram illustrating the advantage of thestructure of pixel unit 211, also illustrated in the above describedFIG. 8A, et cetera.

FIG. 9A shows 1) the use of surface electrode 909 a (i.e., the electrodeA) as a stopper located near elastic hinge 911, which supports mirror913, and 2) the use of surface electrode 909 b of the surface electrode909 b (i.e., the electrode B) and surface electrode 908 a (i.e., theelectrode B′) as stoppers also. In this case, electrode A is placed onsubstrate 901, while electrode B′ is placed under the surface ofsubstrate 901.

If the position of each stopper (i.e., electrode A and B) is at a shortdistance (i.e., a distance d) from elastic hinge 911, the deflectionangle of mirror 913 is determined by h/d. Where “h” is the height of thebase of elastic hinge 911, this calculation is less accurate than when“h” is the height of the electrodes A and B, in which case the accuracyof the calculation is good.

Furthermore, the position of each stopper (i.e., the electrode A or B)is close to elastic hinge 911 and therefore the spring force (i.e., therigidity) of elastic hinge 911 may be decreased to counter stiction(i.e., the force attributable to an intermolecular attraction) betweenmirror 913 and each stopper. This makes possible the advantageousdecrease in size of the mirror element.

FIG. 9B illustrates a stopper placed far from elastic hinge 911 ofelectrodes B and B′.

In this case, if the position of each stopper (i.e., the electrode A orB) is at a far distance (i.e., a distance d′) from elastic hinge 911,the deflection angle of mirror 913 is achieved with greater accuracy.

In order to detach mirror 913 from a stopper 920 by a spring force thatis larger than the stiction between mirror 913 and stopper 920, however,a stronger spring force is required than in the configuration shown inthe above described FIG. 9A.

At the same time, a stronger spring force of elastic hinge 911 will beneeded to increase the voltage applied to electrodes B and B′ to controlmirror 913.

FIGS. 9C and 9D illustrate the placing of electrodes B and B′ onsubstrate 901.

FIG. 9C illustrates the edge (at a distance d1 from elastic hinge 911)of the electrode B functioning as a stopper, while FIG. 9D illustrateselectrode B′ functioning as stopper.

In FIG. 9C, the distance d2 of the edge of electrode B′ from elastichinge 911 is set at a value in order to prevent electrode B′ fromtouching mirror 913.

In contrast, in of FIG. 9D, the distance d1′ of the edge of electrode Bfrom elastic hinge 911 is set at a value smaller than the abovedescribed distance d1, and the distance d2‘of the edge of electrode B’from elastic hinge 911 is set at a value larger than the above describeddistance d2 so that the edge of electrode B′ functions as a stopper formirror 913.

In this case, electrodes B and B′ exist on the substrate 901 andtherefore the voltage applied to electrodes B and B′ decreases as thedistance between mirror 913 and electrodes B/B′ decreases, when the areaof electrodes B and B′ is the same as in the above described FIGS. 9Aand 9B.

In FIGS. 9C and 9D, if the length of elastic hinge 911 is the same, theconfiguration illustrated in FIG. 9C makes it possible to enlarge thearea of electrode B.

In contrast, the area of electrode B′ can therefore be enlarged in theconfiguration shown in FIG. 9D.

As described above, the placement of electrodes on the ON sideseparately according to the present embodiment optimizes the area of theelectrode, the distance between mirror 913 and electrode B (and B′), andthe distance of between electrode B (and B′) and elastic hinge 911. Thisis achieved by using multiple electrodes B and B′, thereby providing alayout to reduce the drive voltage.

With the above described configuration serving as a premise, thefollowing is a description of an exemplary configuration, with referenceto FIG. 10A, of a pixel unit 211 implemented in a pixel array 210 of aspatial light modulator 200 according to the present embodiment.

In contrast to the configuration of pixel unit 211, as illustrated inFIG. 4, described above, in which one pixel is implemented with amirror, two electrodes, and two DRAM-structured memory cells, thepresent embodiment 1 is configured with the addition of plate lines 232(PL-n; where “n” represents the number of ROW lines) to respective ROWlines and interconnect the plate line 232 (PL) and ON electrode 216 byway of a second ON capacitor 233 (Cap 3).

This configuration enables the control of ON electrodes 216 (i.e., B1-1,B1-2 and so on) of the same ROW line even with lines other than bit line(bit line 221-1 and bit line 221-2) and word line 231 (WL-1).

The present embodiment is configured such that the memory cell used forcontrolling mirror 212 is a simple DRAM structure requiring only onetransistor in individual pixel unit 211 constituting the pixel array.Therefore the size of the structure of the memory cell can be kept at aminimum, even if plate line 232 and the second ON capacitor 233 areadded. Therefore, a high resolution is easily achieved through anarrangement of a larger number of pixel units 211 within a pixel arrayof a certain size.

Furthermore, the addition of plate line 232 and second ON capacitor 233makes it possible to greatly expand the gray scale expression through acombination of the ON/OFF control and oscillation control of mirror 212.This achieves a greater gray scale expression than that achieved througha simple PWM control, as described below.

In other words, it is possible to attain both higher definition and ahigher level of gray scale for a projection image by using a spatiallight modulator such as spatial light modulator 200.

The following is a description of an operation of pixel unit 211,configured as shown in FIG. 10A.

On the word line 231 (WL) and plate line 232 (PL), both of which areplaced on the same ROW line, plate line 232 (PL) is made active whenword line 231 (WL) is not selected (L) and when ON electrode 216 isdischarged (e.g., 0 volts).

With this, ON electrode 216 is charged. The charge voltage is determinedby the ratio of the capacitance of ON capacitor 216 b (Cap 2) to that ofthe second ON capacitor 233 (Cap 3). The charge voltage of ON electrode216 is no less than twice the voltage of plate line 232 (PL) when thecapacitance ratio is set at Cap 3>Cap 2.

When word line 231 (WL) is in a selected state (H level), plate line 232(PL) is discharged (e.g., 0 volts).

FIG. 10B is a diagram showing a possible modification of theconfiguration of pixel unit 211 according to the present embodiment.

The configuration shown in FIG. 10B eliminates the ON capacitor 216 b(Cap 2) connected to ON electrode 216 from the configuration illustratedin the above described FIG. 10A.

However, gate transistor 216 c has a floating capacitance Cf at thesource terminal that is connected to ON electrode 216, and the floatingcapacitance Cf produces an effect similar to the effect produced by theeliminated Cap 2.

In this case, the capacitance of the second ON capacitor 233 is set atapproximately the same capacitance as that of OFF capacitor 215 b (i.e.,Cap 3=Cap 1). The floating capacitance Cf is usually very small, makingCap 3>>Cf and, thus, the charge of ON electrode 216 becomes close to thevoltage of plate line 232 (PL).

FIG. 10C is a plain view diagram of an example layout within pixel unit211, of 1) OFF capacitor 215 b in the configuration illustrated in FIG.10B and of 2) second ON capacitor 233 connected to the line 232, withthe same delineations used in FIGS. 8A through 8C.

FIG. 10C is a diagram with a perspective from the top surface of mirror212 (or mirror 913), showing a layer on which upper plate 233 a ofsecond ON capacitor 233 (and OFF capacitor 215 b) are placed.

The upper plate 233 a and lower plate 233 b, which includes the presentsecond ON capacitor 233 are of the same size, with lower plate 233 bplaced right under upper plate 233 a.

Furthermore, the size of upper plate 233 a and lower plate 233 b issmaller than that of mirror 212 (or the mirror 913). This configurationprevents the size of the mirror device from increasing due to the areaof the second ON capacitor 233 jutting out of the contour of mirror 212.

FIG. 10D is a description diagram showing another possible modificationof the configuration of pixel unit 211 shown in the above described FIG.10A.

The modification shown in FIG. 10D is configured with a second OFFcapacitor 234 between plate line 232 and OFF electrode 215, in additionto adding the second ON capacitor 233.

This configuration enables a control of the electric potential on theside of the OFF electrode 215 by way of plate line 232 (PL), thusenabling a diverse control of the mirror 212.

FIG. 10E shows an example configuration in which a second word line231-2 and a second plate line 232-2 are added to the pixel array 210(i.e., the pixel unit 211) illustrated in the above described FIG. 10A.

The configuration of FIG. 10E is such that, in each of multiple pixelunits 211 belonging to the same ROW line (ROW-n), a gate transistor 215c is connected to a word line 231, and a gate transistor 216 c isconnected to a second word line 231-2.

Furthermore, in each of the multiple pixel units 211 belonging to thesame ROW line (ROW-n), the second ON capacitor 233 is connected to plateline 232 or second plate line 232-2, respectively. For example, in pixelunit 1-1, the second ON capacitor 233 is connected to plate line 232,while in next pixel unit 1-2; the second ON capacitor 233 is connectedto second plate line 232-2.

The following is a description of the area around the ON electrode 216of one pixel <pixel 1-1> shown in the above described FIG. 10A, and theoperations of word line 231 (WL-1) and plate line 232 (PL-1) withreference to FIGS. 11A, 11B, 11C, 11D, and 11E.

Referring to FIG. 1A, plate line 232 (PL-1) is at L level (0 volts), and“0” volts of bit line 221-2 (Bitline) is applied to ON electrode 216 bymeans of the H level (5 volts) of word line 231 (WL-1).

In the transition between the states shown in shifting of the state ofFIG. 11A to that of FIG. 11B, in which word line 231 (WL-1) is shiftedto L level (e.g., 0 volts), the gate transistor 216 c is shifted to OFFand ON electrode 216 is separated from bit line 221-2 (Bitline),shifting plate line 232 (PL-1) to H level (e.g., 20 volts), and therebya 10-volt is applied to ON electrode 216 on the basis of the ratio ofthe capacitance (e.g., 1:1) of the second ON capacitor 233 (Cap 3) tothat of ON capacitor 216 b (Cap 2).

FIG. 11D shows an equivalent circuit in the state illustrated in FIG.11B.

Referring to FIG. 11B, while word line 231 (WL-1) remains at L level (0volts), the shifting of plate line 232 (PL-1) to L (0 volts) changes thepotential of ON electrode 216 to 10 volts.

FIG. 11E shows an equivalent circuit in the state illustrated in FIG.11C.

The above description has illustrated one case of Cap 2=15 femto farad(fF) and Cap 3=15 fF; if Cap 2 is only the floating capacitance Cf ofgate transistor 216 c, a voltage close to the potential of plate line232 (PL-1) will be applied to ON electrode 216.

FIG. 12A illustrates a configuration placing the control circuit ofpixel array 210 that arranges pixel units 211 as shown in the abovedescribed FIG. 10A.

In order to control plate line 232, which is added to the configurationof pixel array 210, as illustrated in the above described FIG. 3, aplate line driver unit 250 is added.

That is, the present embodiment is configured so that a plate linedriver unit 250 is added to the area near pixel array 210, in additionto the provision of bit line driver part 220 and word line driver unit230.

Word line driver unit 230 comprises a first address decoder 230 a and aword line driver 230 b, which are used for selecting word lines 231(WL).

Plate line driver unit 250 comprises a plate line driver 251, and plateline address decoders 252-1 and 252-2, all of which are used forselecting plate lines 232 (PL).

Each pixel unit 211 is connected to bit lines 221-1 and 221-2 of the bitline driver unit 220 (bit line driver) so that data is written to pixelunits 211, which belongs to the ROW line selected by a word line 231(WL).

For a word line 231 (WL), externally input serial data WL_ADDR1 is madeparallel to the first address decoder 230 a (WL Address Decoder) and ischanged to a required voltage by word line driver 230 b (WL Driver).

ON electrode 216 of an individual pixel unit 211 is controlled by plateline 232 (PL) separately from word line 231 (WL-1), and, for plate line232 (PL), externally input serial data PL_ADDRa and PL_ADDRb are madeparallel to plate line address decoders 252-1 (PL Address Decoder-a) and252-2 (PL Address Decoder-b), respectively, so that either value isconverted by plate line driver 251 (PL Driver) to the required voltage.

Here, the number of ROM lines comprising multiple pixel units 211 on onehorizontal line can be, for example, 720 lines or more.

In such a case, each data signal input to memory cells M1 and M2 fromthe bit line 221-1 and 221-2, respectively, is transmitted to individualpieces of memory on one ROW line at the speed of 23 nanoseconds (nsec.)or slower.

That is, in order to process 720 ROW lines by dividing and assigning adisplay period into four colors (red (R), green (G), blue (B) and white(W)) at the rate of 60 frames per second, with each color in 256-bitgray scale, the transmission speed is as follows:

1/60 [sec]/4 [divisions]/256 [bit gray scale]/720 [lines]=22.6 nsec.

Furthermore, in order to process 1080 ROW lines by dividing andassigning a display period into three colors (R, G and B) at the rate of60 frames per second, with each color in 256-bit gray scale, thetransmission speed is as follows:

1/60/3/256/1080=20 nsec.

FIG. 12B is a conceptual diagram illustrating the internal configurationof plate line driver 251 (PL Driver) shown in the above described FIG.12A.

The internal configuration of plate line driver 251 (PL Driver)comprises circuits provided to correspond to plate lines 232 (PL).

In plate line driver 251, an OR circuit 251 a is equipped at the initialstage so as to enable either plate line address decoder 252-1 (PLAddress Decoder-a) or plate line address decoder 252-2 (PL AddressDecoder-b) to select a plate line 232 (PL).

The output of OR circuit 251 a is input to flip-flop 251 b (Flip-Flop)and the output value is retained therein.

Then, the output value is latched at latch 251 c (Latch) with a WL-CLKin order to synchronize with bit line driver part 220 (bit line driver).It is then converted by level shift circuit 251 d (Level shift) into therequired voltage for applying to ON electrode 216.

FIG. 12C illustrates the internal configuration of the plate lineaddress decoder 252-1 (PL Address Decoder-a) shown in the abovedescribed FIG. 12A.

Plate line address decoder 252-1 comprises 1) a serial-parallelconversion circuit 252 a for the serial-to-parallel conversion of anexternal serially input address signal (PL_ADDRa) into the number ofbits of plate lines 232, and 2) an address detection unit includes EXORcircuits 252 b and NOR circuits 252 c, all of which are implemented forthe number of bits of PL_ADDRa.

An externally input address signal (PL_ADDRa) is serial-to-parallelconverted by serial-parallel conversion circuit 252 a and is inputted inparallel to the respective EXOR circuits 252 b.

If a plate line (PL) is the same as a plate line 232 (PL) selected bythe parallel-converted value, the present PL is selected by the addressdetection unit (i.e., the EXOR circuit 252 b and NOR circuit 252 c)corresponding to individual plate line 232.

Although not specifically shown in a drawing, the internalconfigurations of plate line address decoder 252-2 (PL AddressDecoder-b) and the first address decoder 230 a (WL Address Decoder) canbe similar to that of the above described plate line address decoder252-1.

FIG. 12D is a diagram showing an exemplary modification configured byadding a function to the address decoder shown FIG. 12C as describedabove.

If the number of plate lines 232 (PL) is, for example, 1080, the bitwidth required for the serial input of the PL_ADDRa is 11 bits. In thiscase, there is a surplus of 967 (=2047 (i.e., 11 bits)−1080).

Then, if there is an address input (PL_ADDRa) of 1080 or more, thoseaddresses are detected and all plate lines 232 (PL) are selected in thiscase, and thereby reset operations of pixel unit 211 can be performed.

For this purpose, FIG. 12D shows a circuit that further includes an ORcircuit 252 d for taking the logic sum of the outputs of all addressdetection units, in addition to being equipped with the addressdetection units (i.e., the EXOR circuits 252 b and NOR circuits 252 c)corresponding to surplus address values.

This circuit as shown can detect surplus address(es) if there is aninput of 1080 addresses or more and to select all plate lines 232 (PL)at the OR circuit 252 d, thereby enabling a reset operation of pixelunit 211.

FIG. 12E is a diagram illustrating the internal configuration of bitline driver unit 220 (Bitline Driver) shown in the above described FIG.12A.

Bit line driver unit 220, according to the present embodiment, comprisesa first stage latch 220 a, a second stage latch 220 b, a level shiftcircuit 220 c, a third stage latch 220 d, an inverter 110 e, and a modechangeover switch 220 f.

The inverter 110 e and mode changeover switch 220 f function as a columndecoder for controlling bit lines 221-1 and 221-2.

That is, inverter 220 e logically inverts the output (latch out) fromthird stage latch 220 d to branch out as a bit line 221-1, while modechangeover switch 220 f turns ON/OFF the latch out output to thepre-branched bit line 221-2.

If one ROW is, for example, 1920 bits, bit line driver part 220 receivesan external input that is 15 times 128-bit pixel data.

Bit line driver part 220 latches this volume of data in three stages asfollows:

First stage: 128 latches (at the first stage latch 220 a)

↓

Second stage: 640 latches (at the second stage latch 220 b)

↓

Voltage conversion (level shift) (at the level shift circuit 220 c)

↓

Third stage: 1920 latches (at the third stage latch 220 d)

As such, after performing 1920 latches at the third stage latch 220 d,and when the data is sent to the ON side (i.e., the bit line 221-2) andOFF side (i.e., the bit line 221-1) of the bit line, the respectivelogic states of bit line 221-1 and bit line 221-2 are determined by ajudgment logic on the basis of the truth table shown in FIG. 12F.

FIG. 13 is a timing chart depicting the relationship between (i) and(ii), where (i) is the operation timing of the <pixel 1-1> (i.e., pixelunit 211) and <pixel 1-2> (i.e., pixel unit 211) belonging to the sameROW line, and (ii) is the behavior of mirror 212 in pixel array 210shown in the above described FIG. 10A.

In this case, the respective display states of the two pixel units 211are a gray display for the <pixel 1-1> and a black display for the<pixel 1-2>.

The <pixel 1-1> and <pixel 1-2> belong to the same ROW line andtherefore the mode changeover signal 221-3 (Intermediate), word line 231(WL-1), and plate line 232 (PL-1) are common signals.

In the example shown in FIG. 13, the signal (WL) on a word line 231operates during a predetermined interval (i.e., one cycle of an intervalbetween a control timing t1 and a control timing t4 in this case) inorder to carry out the selection control of bit line 221-1 and bit line221-2.

In contrast, the signal (PL) on plate line 232 operates during aninterval (i.e., control timing t1 and control timing t2) that is shorterthan one cycle of the signal (WL) on a word line 231.

For example, the signal (PL) operates at two consecutive times (refer tothe changes in the potentials 232 a that is turned ON with the pulse ofplate line address decoder 252-1 and turned OFF with the pulse of plateline address decoder 252-2) within the period of one cycle of word line231 in the example shown in FIG. 13.

Therefore, the transmission speed (i.e., the frequency) of a signal onplate line 232 is faster than the transmission speed (i.e., thefrequency) of a signal on word line 231.

Until control time t1, the mirror 212 of the <pixel 1-1> is stationarilydeflected to the side of ON electrode 216 if the Latch OUT (i.e., theoutput of the third stage latch 220 d) is “1” and to the side of OFFelectrode 215 if the Latch OUT is “0”. That is, until control time t1,the operation of mirror 212 is controlled by means of a pulse widthmodulation (PWM) in accordance with a PWM control profile 451.

Immediately prior to control time t1, mirror 212 is stationarilydeflected to the side of ON electrode 216; then, at control time t1, themode changeover signal 221-3 (Intermediate) is turned to be “H”, and(although the latch OUT is “1”) OFF electrode 215 and ON electrode 216are turned to be “0” volts, prompting mirror 212 to start a freeoscillation.

At control time t2, plate line 232 (PL-1) is selected by plate lineaddress decoder 252-1 (PL Address Decoder-a) and PL-1 is turned to be anH level potential 232 a (i.e., a potential higher than the H levelpotential 221 a of bit line 221 (bit line).

At control time t3, plate line 232 (PL-1) is selected by plate lineaddress decoder 252-2 (PL Address Decoder-b) and plate line 232 isturned to be L level.

During the period between control time t2 and t3, mirror 212 is drawnback to the side of ON electrode 216 and starts an intermediateoscillation (OSC) as shown by an intermediate oscillation controlprofile 452.

Then, at control time t5, after control time t4, an “H” is set by bitline 221-1 (Bitline) at the side of OFF electrode 215, and mirror 212 isdrawn to OFF electrode 215 to be stationary in the OFF state.

Meanwhile, the mirror 212 of the <pixel 1-2> must be continuouslystationary on the side of OFF electrode 215, in order to display black.

Plate line 232 (PL-1) is common to the <pixel 1-2> and <pixel 1-1>, andtherefore during the period between control time t2 and t3, a voltage(i.e., potential 221 a) is generated at ON electrode 216. However,mirror 212 is stationary on the OFF side and the distance between ONelectrode 216 and mirror 212 is far, and therefore the Coulomb forceapplied to the mirror 212 is weak and the position thereof will not bechanged.

Note that the interval between control time t1 and t2 (i.e., apredetermined delay time) can be set to be the same (i.e., constant)within one frame.

Furthermore, the above described predetermined delay time can bedetermined by the intensity of illumination light or the quantity ofreflection light of mirror 212 of a pixel unit 211.

Note that, in FIG. 13, the intermediate oscillation starts at a PWM ON.If it starts at OFF, the method comprises 1) connecting plate line (232)to the memory on the OFF side, 2) connecting the capacitor of the ONside memory to the ground, 3) setting the potential of the electrodeA1-1 at “H” and the potential of the electrode B1-1 at “L” at the timingt1, and 4) applying a voltage to the electrode A1-1 from the plate line(232) at control time t2 and t3.

FIG. 14 is a timing chart of the ROW lines and address decoder which areshown in FIG. 12A.

In FIG. 14, control times t1, t2, t3, and t4 correspond to times t1through t4 as shown in FIG. 13.

On ROW 1, at control time t1, word line 231 (WL-1) carries out dataloading and then first address decoder 230 a(WL_ADDR1) selects ROW 2, 3,4 through 1080 sequentially to carry out data loading.

At control time t2, plate line address decoder 252-1 (PL_ADDRa) selectsplate line 232 (PL-1).

Plate line address decoder 252-1 (PL_ADDRa) selects PL-2, 2-3, 2-4through 2-1080 sequentially.

At control time t3, plate line address decoder 252-2 (PL_ADDRb) selectsplate line 232 (PL-1).

Plate line address decoder 252-2 (PL_ADDRb) selects PL-2, 2-3, 2-4through 2-1080 sequentially.

As such, the control of the intermediate oscillation of all ROW lines isenabled in the minimum interval (i.e., during the period between controltime t1 and t4) of data loading performed by word line 231 (WL).

FIG. 15 is a conceptual diagram showing another possible modification ofpixel unit 211.

FIG. 15 shows a second ON electrode 235 (i.e., an electrode C) connecteddirectly to plate line 232, in addition to comprising the ON electrode216 (i.e., the electrode B).

That is, in contrast to the configuration of controlling ON electrode216 by means of plate line 232 (PL), as shown in the above describedFIG. 12A (in which two electrodes, that is, OFF electrode 215 and ONelectrode 216, are equipped for one pixel) pixel unit 211, as shown inFIG. 15, has a second ON electrode 235 (i.e., an electrode C) andconnects plate line 232 (PL) directly to the electrode C without theintervention of a circuit element.

The drive circuit for pixel unit 211 shown in FIG. 15 is the same asthat shown in FIG. 12A.

FIGS. 15A and 15B are cross-sectional diagrams of a pixel unit 211, inan ON state and an OFF state, respectively, comprising two electrodes,i.e., an ON electrode 216 and a second ON electrode 235, on the ON sideillustrated in FIG. 15.

Note that the delineation symbols used in FIGS. 15A and 15B are the sameas those described in FIG. 8A.

FIGS. 15C and 15D are plain view diagrams showing possible layouts ofthe added second ON electrode.

The configuration of FIG. 15D shows surface electrodes 909 b and 908 a,which includes the ON electrode 216 in the configuration shown in theabove described FIG. 8B, electrically mutually independent and connectedto plate line 232 (PL), and thereby the function of the second ONelectrode 235 (i.e., the electrode C) is achieved.

Furthermore, FIG. 15D shows a configuration in which surface electrode908 a, of surface electrodes 909 b and 908 a of above described FIG. 8C,is eliminated and the area of surface electrode 909 b is enlarged anddivided into two parts. Thereby the function of ON electrode 216 (i.e.,the electrode B) and second ON electrode 235 (i.e., the electrode C) areachieved.

FIG. 15E is a plain view diagram showing another possible layout ofelectrode B connected to word line 231 and electrode C connected toplate line 232. FIG. 15F is a cross-sectional diagram.

Electrode C (i.e., surface electrode 908 a), which is connected to plateline 232, is placed near elastic hinge 911 in a rectangular-shapedcharacter “C” so as to surround elastic hinge 911. Additionally,electrode B, which is connected to word line 231, is placed so as tosurround three sides of electrode C.

FIG. 15G is configured, in pixel unit 211 shown in the above describedFIG. 15, with the additional of a second ON capacitor 217 b and a secondON gate transistor 217 c, both of which are used to control second ONelectrode 235. A second plate line 232-2 is also added.

Additionally, the second ON capacitor 217 b is connected to plate line232, and the second ON capacitor 217 b is also connected to the newlyadded second plate line 232-2.

FIG. 15H differs from FIG. 15G in that the configuration of FIG. 15H isequipped with a second word line 231-2 instead of second plate line232-2.

Furthermore, the gate of the second ON gate transistor 217 of the secondON electrode 235 is connected to, and controlled by, the second wordline 231-2.

FIG. 16 is a timing chart showing 1) the operation timings of the <pixel1-1> and <pixel 1-2>, both of which belong to the same ROW line, and 2)the operation of mirror 212 in pixel unit 211, which is equipped withthe second ON electrode 235 shown in the above described FIG. 15.

Additionally, the <pixel 1-1> displays gray, while the <pixel 1-2>displays black.

Since the two belong to the same ROW line, the mode changeover signal221-3 (Intermediate), word line 231 (WL-1), and plate line 232 (PL-1)are common signals to the <pixel 1-1> and <pixel 1-2>.

In contrast to the timing chart shown in the above described FIG. 13,the chart shown in FIG. 16 are the waveforms of ON electrode 216 (i.e.,the electrode B) and second ON electrode 235 (i.e., the electrode C)when attracting mirror 212 from the ON state to the oscillation state.

That is, in FIG. 16, mirror 212 is attracted to the oscillation state bychanging the potential of second ON electrode 235 (i.e., the electrodeC) to a potential 232 a by plate line 232, instead of changing thepotential of ON electrode 216.

As such, in this configuration the second ON electrode 235 is equippedin addition to ON electrode 216, and the potential of the second ONelectrode 235 is controlled by plate line 232 as shown in FIG. 15, etcetera. This makes it possible to apply a voltage to the second ONelectrode 235 independent from the signals from bit lines 221-1 and221-2, thus enabling a more accurate control of operations than thecontrol by means of only word line 231 or the like.

Furthermore, control by plate line 232 makes it possible to havemultiple voltages applied to the address electrodes, such as the secondON electrode 235 and ON electrode 216, thereby attaining a more complexoperation control.

This configuration enables a sufficient level of drive voltage formemory cell M2 and control of the high-speed timing for applying thevoltage, thereby attaining a high-speed operation control for mirror212.

Incidentally, bit data is ignored in the example configuration shown inFIG. 15, and, therefore, the drive voltage is increased for each line ofplate lines 232. In this case, such a lump control for each line ofplate lines 232 does not create a problem because it is an amplitudeadjustment in the oscillation control for mirror 212.

FIGS. 17A, 17B, 17C, 17D, and 17E are timing diagrams for showingvarious exemplary PWM control profile 451 (PWM) (i.e., a PWM drivetiming 440) and an intermediate oscillation control profile 452 (OSC)(i.e., an OSC drive timing 441) in mirror control profile 450 for oneframe period of a mirror.

The mirror control profile shown in FIG. 17A illustrates the generationof a PWM control profile 451 and an intermediate oscillation controlprofile 452 sequentially, in the latter part of one frame.

FIG. 17B illustrates the generation of PWM control profile 451 at thebeginning of one frame and generation of intermediate oscillationcontrol profile 452 toward the end of one frame.

FIG. 17C illustrates the case of generation intermediate oscillationcontrol profile 452 during the first half of one frame and then thegeneration of PWM control profile 451.

FIG. 17D illustrates the case of generation intermediate oscillationcontrol profile 452 at the start of one frame and the generation of PWMcontrol profile 451 at the end of the frame.

FIG. 17E illustrates the aligning of the ON position of PWM controlprofile 451 with the beginning of one frame and the aligning of the endof intermediate oscillation control profile 452 with the end of oneframe.

The pattern (i.e., the intermediate oscillation control profile 452) ofmirror 212 of the pixel displaying gray (i.e., <pixel 1-1>) shown in theabove described FIGS. 13 and 16 corresponds to the above described FIG.17A.

Note that the present embodiment is also configured to be capable ofchanging oscillation states in the midst of an intermediate oscillation(i.e., the intermediate oscillation control profile 452).

FIGS. 17F and 17G show the operation of mirror 212 when a voltage isre-applied, from plate line 232 (PL), to ON electrode 216 (i.e., theelectrode B) in the midst of an intermediate oscillation, for example,under the control shown in FIG. 13.

Referring to FIGS. 17F and 17G, a re-application voltage is generated atON electrode 216 at control time t6, so that the waveforms of theintermediate oscillation are changed by the timing of the application,the period of time of the application, and the voltage of there-application.

In FIG. 17F, the period of application time of the re-applicationvoltage 221 b is relatively small and therefore the center of theoscillation of mirror 212 does not change and only the amplitude becomessmaller.

In contrast, FIG. 17G shows that the period of application time of there-application voltage 221 b is relatively large and therefore thecenter of the oscillation of mirror 212 is biased to the ON side insteadof the center.

FIG. 18 illustrates the placing of a diode 236 in place of the second ONcapacitor 233 in the configuration of pixel unit 211 as shown in theabove described FIG. 10A.

The drive circuit for pixel unit 211 in this case is the same as FIG.12A. The drive timing, however, uses bit line 221-1 (bit line) at theend of returning the mirror 212 as described below.

FIG. 19 is a timing chart illustrating the operation of mirror 212 andthe operation timing of the <pixel 1-1> and <pixel 1-2> that belong tothe same ROW line of the pixel array 210 as shown in FIG. 18.

Also, in this case, of the two pixel units 211 in focus, the <pixel 1-1>displays gray, while the <pixel 1-2> displays black.

Since the two belong to the same ROW line, the mode changeover signal221-3 (Intermediate), word line 231 (WL-1), and plate line 232 (PL-1)are common signals to the <pixel 1-1> and <pixel 1-2>.

The example control shown in FIG. 19 differs from the example controlshown in the above described FIG. 13 since the former discharges ONelectrode 216 at control time t3 with bit line 221-1 (bit line) and wordline 231 (WL) (refer to the waveform at control time t3 in word line231).

Therefore, only one PL Address Decoder (i.e., plate line address decoder252-1 and plate line address decoder 252-2) is required.

FIG. 20 illustrates the connection between the address decoder and bitline driver part 220 (bit line driver) that are used for selecting wordline 231 (WL) and plate line 232 (PL) of pixel array 210.

As shown in FIG. 20, this is a simple configuration connecting one plateline address decoder 252 to plate line driver 251, in place ofconnecting two plate line address decoders 252-1 and 252-2 thereto.

FIG. 21 shows another possible modification of the configuration ofpixel unit 211 according to the present embodiment.

The configuration shown in FIG. 21 places a field effect transistor 237(FET) in place of second ON capacitor 233 in the configuration of pixelunit 211 shown in the above described FIG. 10A.

That is, plate line 232 is connected to the gate electrode of fieldeffect transistor 237, and the applied voltage from plate line 232controls whether or not a power source voltage Vcc (to which the drainof field effect transistor 237 is connected is) is applied to ONcapacitor 216 b.

The drive circuit for pixel unit 211 according to the examplemodification shown in FIG. 21 is the same as that of the above describedFIG. 12A.

The drive time of pixel unit 211, comprising field effect transistor237, is controlled in the same manner as that of the circuit shown inFIG. 12A, where the setup voltage from plate line 232 (PL) to ONelectrode 216 is determined by the power source voltage Vcc, to whichthe drain of the FET is connected, instead of being determined by thevoltage of plate line 232 (PL).

FIG. 22A is a conceptual diagram showing an example modification of theconfiguration of pixel array 210 according to the present embodiment.

The configuration illustrated in FIG. 22A divides multiple ROW lines(ROW-1 through ROW-1080) into upper and lower groups (i.e., an upper rowline area 210 a and a lower row line area 210 b, each comprising anupper bit line driver part 220-1 and a lower bit line driver part 220-2(bit line Driver), a first address decoder 230 a, a word line driver 230b (WL Address Decoder_up and WL Driver-up, WL Driver_down and WLDriver_down), a plate line driver 251-1, a plate line address decoder252-1, and a plate line address decoder 252-2 (PL Address Decoder-a-upand PL Driver-up, PL Address Decoder-a_down, b_down and PL Driver-up,down)).

Specifically, multiple row lines are divided into the upper row linearea 210 a including row lines ROW-1 through ROW-540, and the lower rowline area 210 b that includes row lines ROW-541 through ROW-1080.

In this case, the level change (i.e., the potential 232 a) of plate line232 is accomplished by plate line address decoder 252-1 changing it to Hlevel and plate line address decoder 252-2 changing it to L level.

FIG. 22B shows an example configuration in which plate line driver 251-1(PL Driver_up) and plate line driver 251-2 (PL Driver_down) that areequipped for the upper and lower ROW line groups, each equipped with oneplate line address decoder 252 (PL Address Decoder-up) and one plateline address decoder 252 (PL Address Decoder_down) in the comprisal ofpixel array 210 as shown in the above described FIG. 22A.

In this case, the level change (i.e., the potential 232 a) of plate line232 (PL) is carried out by plate line 232 (PL).

FIG. 22C illustrates the configuration in which a first address decoder230 a and a word line driver 230 b, a plate line driver 251 and a plateline address decoder 252-1, and a plate line address decoder 252-2 areequipped commonly for each group in the configuration in which multipleROW lines of a pixel array 210 is divided into the upper and lowergroups. Each of the upper and lower ROW line groups is equipped withupper bit line driver part 220-1 and lower bit line driver part 220-2.

In this case, the ROW lines (both upper and lower) applicable to thesame address are driven simultaneously. The combination of therespective ROW lines in the upper and lower groups to be simultaneouslydriven is determined by wirings.

For example, the ROW lines applicable to the same address (in theexample of FIG. 22C, the first ROW-1 in the upper group and the firstROW-541 in the lower group) are simultaneously driven.

FIG. 22D shows an example configuration in which plate line driver 251commonly equipped in the upper and lower groups is separated into aplate line driver 251-1 (PL Driver_up) corresponding to the upper groupand a plate line driver 251-2 (PL Driver_down) corresponding to thelower group. The divided drivers are placed correspondingly at therespective groups, according to the configuration of pixel array 210shown in FIG. 22C.

In this case, the ROW lines belonging to the upper and lower groups areindividually driven, unlike the configuration shown in the abovedescribed FIG. 22C.

FIG. 23A is a cross-sectional diagram showing an example modification ofthe configuration of a pixel unit 211 (i.e., a mirror element 4011)according to the present embodiment. FIG. 23B is a conceptual diagramshowing an example configuration of the drive circuit for the pixelunit.

Mirror element 4011 (i.e., pixel unit 211) according to the presentembodiment comprises a hinge electrode 4009 and an address electrode4013, both of which are placed on a device substrate 4004 and coveredwith an insulation layer 4006.

A mirror 4003 is supported on insulation layer 4006 of hinge electrode4009 by way of an elastic hinge 4007. In this case, mirror 4003 issupported as a cantilever against elastic hinge 4007, with the entiretyof the mirror 4003 protruding over an address electrode 4013.

Furthermore, a stopper 4002 is placed on the other side of the addresselectrode 4013 across from the elastic hinge 4007, with the lower edgeof the stopper 4002 fixed onto the device substrate 4004.

Furthermore, mirror 4003 is tilted to close to address electrode 4013 bya Coulomb force resulting from an application of a voltage V1 to addresselectrode 4013. Mirror 4003 is stopped at a position abutting oninsulation layer 4006 covering address electrode 4013 (which is calledan ON state).

Furthermore, when the application of voltage V1 to address electrode4013 is cut off, mirror 4003 is restored by the elasticity of elastichinge 4007 to its horizontal position, abutted by the stopper 4002 sothat it does not move beyond this state (which is called an OFF state).

The following is a description of a control circuit for mirror element4011, as illustrated in FIG. 23B. In this case, mirror element 4011 issupported by elastic hinge 4007 in a cantilever and therefore is aconfiguration equipped with bit line 221-2, gate transistor 216 c, ONcapacitor 216 b, and word line 231, which are the circuit elements ofmemory cell M2 on the ON side, included in the circuit configurationshown in the above described FIG. 10A.

Furthermore, as shown in FIG. 10A, the present embodiment is equippedwith plate line 232, in addition to word line 231, and connects plateline 232 to address electrode 4013 by way of the second ON capacitor233.

Further, with the control using word line 231, plate line 232 and bitline 221-2, the OFF state, ON state, and the intermediate oscillationstate that is between the ON state and OFF state, are achieved asdescribed below.

The following is a description of an example method for controllingpixel array 210 comprising the cantilever-structured mirror 4003 asshown in the above described FIGS. 23A and 23B.

Note that the control system can use the configuration, as is, as shownin FIG. 12A.

FIG. 24 is a circuit diagram illustrating in detail a part of the layoutof pixel array 210 comprising a mirror 4003 (shown in the abovedescribed FIG. 23B) that is structured as a cantilever.

FIG. 25 is a timing chart depicting the operation of the mirror and theoperation timings of the <pixel 1-1> and <pixel 1-2> belonging to thesame ROW line as that of FIG. 24.

The example shown in FIGS. 24 and 25 presupposes that the <pixel 1-1>displays gray, while the <pixel 1-2> displays black.

In this case, since the <pixel 1-1> and <pixel 1-2> belong to the sameROW line, the mode changeover signal 221-3 (Intermediate), word line 231(WL-1), and plate line 232 (PL-1) are common signals to the two of them.

Until control time t1, mirror 4003 of the <pixel 1-1> is in PWMoperation and a voltage V1 in accordance with bit line 221 (bitline) isapplied to the electrode.

Specifically, if the voltage at bit line 221 (bitline) is at the Hlevel, mirror 4003 is drawn to address electrode 4013 so as to abut ontoinsulation layer 4006 of address electrode 4013 and is stationary. Thisis an ON state.

If the potential at bit line 221 (bitline) is L level, mirror 4003separates from address electrode 4013, abuts on stopper 4002 and stopsthereat. This is an OFF state.

Just prior to control time t1, mirror 4003 is stationary in the ONstate, that is, abutting on address' electrode 4013. At control time t1,address electrode 4013 is changed by bit line 221 (bitline) to be “0”volts (i.e., discharged), and mirror 4003 starts to separate fromaddress electrode 4013 by means of the elasticity of elastic hinge 4007.

At control time t2, that is, before mirror 4003 is far from addresselectrode 4013, plate line address decoder 252-1 (PL Address Decoder-a)selects plate line 232 (PL-1), and plate line 232 (PL-1) is changed to Hlevel (i.e., a potential 232 b, which is lower than the H level of bitline 221). A voltage is generated at the electrode by the potential 232b so that mirror 4003 is attracted by address electrode 4013 and isstationary thereat.

At control time t3, the plate line address decoder 252-2 (PL AddressDecoder-b) selects plate line 232 (PL-1) and, if it is L level, mirror4003 starts to separate from address electrode 4013 again.

At control time t4, that is before mirror 4003 is far from addresselectrode 4013, as at t2, the plate line address decoder 252-2 (PLAddress Decoder-a) selects plate line 232 (PL-1) and is changed to Hlevel (i.e., the potential 232 b) and mirror 4003 is re-attracted toaddress electrode 4013 and is stationary thereat.

At control time t5, the plate line address decoder 252-2 (PL AddressDecoder-b) selects plate line 232 (PL-1), and the PL-1 is changed to Llevel so that mirror 4003 is re-attracted by address electrode 4013 tobe stationary thereat. Simultaneously, or a little thereafter, a memorycell is selected by word line 231, and “0” volts are set by bit line221.

With this series of operation, mirror 4003 able 1) to generate a smallerquantity of light than the quantity during the minimum data-loadingperiod in accordance with a PWM control with word line 231 (WL) and 2)to express an intermediate gray scale.

In this case, the mirror of the <pixel 1-2> adjacent to the <pixel 1-1>displays black and therefore the mirror needs to be continuouslystationary on the side of stopper 4002 (i.e., the OFF side).

Plate line 232 (PL-1) is common to the <pixel 1-1> and <pixel 1-2> andtherefore, between control times t2 and t5, a voltage is generated ataddress electrode 4013. However, mirror 4003 is stationary on the OFFside and the distance between address electrode 4013 and mirror 4003 isfar, and, therefore, a Coulomb force applied to mirror 4003 is small,causing no change to the position of mirror 4003.

That is, the control is such as to maintain the following relationshipin order not to change the position of mirror 4003:

[H level (V1) of the bit line 221 (Bitline)]>[H level (V2) of the PL]

As such, spatial light modulator 200 comprising mirror element 4011,configured as shown in FIGS. 23A and 23B, is configured to controlmirror element 4011 with one memory cell M2, thereby making it possibleto make the size of the mirror element 4011 more compact and expressvarious gray scale by means of the intermediate oscillation of mirror4003, in addition to the ON and OFF states, using plate line 232.

In a projection technique using spatial light modulator 200, a reductionin the size of mirror element 4011 makes it possible to obtain both ahigher level of definition of the projection image by arraying a largernumber of mirror elements 4011 and a higher grade of gray scale with theintermediate oscillation of mirror 4003 using plate line 232.

FIG. 26A is a plain view diagram illustrating the packaging structure ofa package accommodating the spatial light modulator shown in the abovedescribed FIGS. 22A through 22D, et cetera. FIG. 26B is itscross-sectional diagram.

The spatial light modulator 200 according to the present embodimentplaces the upper bit line driver part 220-1 and lower bit line driverpart 220-2 along the upper and lower sides, respectively, which areparallel to the ROW line in the surrounding area of pixel array 210, andplaces word line driver unit 230 and plate line driver unit 250 alongthe left and right sides, respectively, which cross the aforementionedupper and lower sides.

The spatial light modulator 200 is accommodated in the concave part 201a of package 201.

Multiple bonding pads 202 are placed in the surrounding area of theconcave part 201 a of package 201.

Bit lines and address lines placed in the upper bit line driver part220-1, lower bit line driver part 220-2, word line driver unit 230, andplate line driver unit 250 are connected, by way of bonding wires, tobonding pads 202 provided in the surrounding area, and are furtherconnected electrically, by way of external connection electrodes (whichare not shown in a drawing here) that are placed on the bottom part ofthe package 201, to the wiring board or the like of a projectionapparatus (which is described below) incorporating package 201.

The following is a description of an example configuration of aprojection apparatus comprising spatial light modulator 200 equippedwith the above described plate line 232. Note that the constituentcomponent corresponding to the previously described constituentcomponent is noted in the drawing with a corresponding sign inparenthesis as appropriate.

FIG. 27 is a conceptual diagram showing the configuration of aprojection apparatus according to a preferred embodiment of the presentinvention.

As shown in FIG. 27, a projection apparatus 5010 according to thepresent embodiment comprises a single spatial light modulator (SLM) 5100(i.e., the spatial light modulator 200), a control unit 5500 (i.e., thecontrol apparatus 300), a Total Internal Reflection (TIR) prism 5300, aprojection optical system 5400, and a light source optical system 5200.

The spatial light modulator 5100 is implemented according to theabove-described spatial light modulator 200 comprising plate line 232.

The projection apparatus 5010 is generally referred to as a single-panelprojection apparatus 5010 implemented with a single spatial lightmodulator 5100.

The projection optical system 5400 is equipped with spatial lightmodulator 5100 and TIR prism 5300 in the optical axis of projectionoptical system 5400, and the light source optical system 5200 isequipped in such a manner that the optical axis thereof matches that ofprojection optical system 5400.

The TIR prism 5300 causes 1) an illumination light 5600 from lightsource optical system 5200, which is placed onto the side, to enterspatial light modulator 5100 at a prescribed inclination angle relativethereto as incident light 5601 and 2) a reflection light 5602 reflectedby spatial light modulator 5100 so as to reach projection optical system5400.

The projection optical system 5400 projects reflection light 5602, asprojection light 5603, by way of spatial light modulator 5100 and TIRprism 5300 to a screen 5900 or the like.

The light source optical system 5200 comprises an adjustable lightsource 5210 for generating illumination light 5600, a condenser lens5220 for focusing illumination light 5600, a rod type condenser body5230, and a condenser lens 5240.

The adjustable light source 5210, condenser lens 5220, rod typecondenser body 5230, and condenser lens 5240 are sequentially placed inthe aforementioned order on the optical axis of illumination light 5600emitted from adjustable light source 5210 and incident to the side faceof TIR prism 5300.

The projection apparatus 5010 employs a single spatial light modulator5100 for implementing a color display on the screen 5900 by means of asequential color display method.

That is, adjustable light source 5210, comprising a red laser lightsource 5211, a green laser light source 5212, and a blue laser lightsource 5213 (which are not shown in a drawing here), which allowsindependent controls for the light emission states, performs theoperation of dividing one frame of display data into multiple sub-fields(i.e., three sub-fields, that is, red (R), green (G) and blue (B) in thepresent case) and causes the red laser light source 5211, green laserlight source 5212, and blue laser light source 5213 to emit eachrespective light in at the time frame corresponding to the sub-field ofeach color as described below.

FIG. 28 is a block diagram showing an example configuration of controlunit 5500 comprised in the above described single-panel projectionapparatus 5010. Control unit 5500 comprises a frame memory 5520, an SLMcontroller 5530, a sequencer 5540, a video image analysis unit 5550, alight source control unit 5560, and a light source drive circuit 5570.

The sequencer 5540 implements a microprocessor and the like, controlsthe operation timing and the like of the entirety of control unit 5500and spatial light modulator 5100.

The frame memory 5520 retains, for example, the equivalent to one frame,input digital video data 5700 (i.e., a binary video image signal 400)from an external device (not shown in a drawing herein) that isconnected to a video signal input unit 5510. The input digital videodata 5700 is updated, moment-by-moment, every time the display of oneframe is completed.

The SLM controller 5530 processes the input digital video data 5700 readfrom the frame memory 5520 as described below, separating the read datainto multiple sub-fields, and outputs them to the spatial lightmodulators 5100 as control data used for implementing the ON/OFF controland oscillation control (which are described below) of a mirror 5112 ofspatial light modulator 5100.

The sequencer 5540 outputs a timing signal to the spatial lightmodulators 5100 synchronously with the generation of data at the SLMcontroller 5530.

The video image analysis unit 5550 outputs a video image analysis signal6800 used for generating various light source pulse patterns on thebasis of the input digital video data 5700 inputted from the videosignal input unit 5510.

The light source control unit 5560 controls, by way of the light sourcedrive circuit 5570, the operation of adjustable light source 5210emitting illumination light 5600 on the basis of the video imageanalysis signal 6800 obtained from the video image analysis unit 5550 byway of the sequencer 5540.

The light source drive circuit 5570 drives the red laser light source5211, green laser light source 5212, and blue laser light source 5213 ofadjustable light source 5210 to emit light on the basis of aninstruction from the light source control unit 5560.

FIG. 29 is a conceptual diagram showing another exemplary modificationof a multi-panel projection apparatus according to the presentembodiment.

The projection apparatus 5040 is configured so that multiple to placespatial light modulators 5100 (i.e., the spatial light modulator 200)corresponding to the three respective colors R, G and B, so as to beadjacent to one another in the same plane on one side of a lightseparation/synthesis optical system 5330.

This configuration makes it possible consolidate spatial lightmodulators 5100 into the same packaging unit, for example, a package 201or the like, and thereby save space.

The light separation/synthesis optical system 5330 comprises a TIR prism5331, a TIR prism 5332, and a TIR prism 5333.

TIR prism 5331 has guides to spatial light modulators 5100 illuminationlight 5600, incident in the lateral direction of the optical axis ofprojection optical system 5400, as incident light 5601.

TIR prism 5332 separates a red color light from the incident light 5601and guides it to the red color-use spatial light modulator 5100, andalso captures reflection light 5602 of the separated incident light andguides it to projection optical system 5400.

Likewise, TIR prism 5333 separates the incident lights of green and bluecolors from incident light 5601, makes them incident to the individualspatial light modulators 5100, equipped correspondently to theirrespective colors, and captures reflection lights 5602 of the respectivecolors and guides them to projection optical system 5400.

FIG. 30 is a block diagram showing an example configuration of thecontrol unit of a multi-panel projection apparatus according to thepresent embodiment.

Control unit 5502 comprises SLM controllers 5531, 5532, and 5533, whichare used for controlling each of the spatial light modulators 5100equipped for the colors R, G and B. The comprisal of the controllers isdifferent from the above described control unit 5500, which is otherwisesimilar.

That is, SLM controller 5531, SLM controller 5532, and SLM controller5533 correspond to their respective color-use spatial light modulators5100, which are formed on the same substrates as those of theirrespective spatial light modulators 5100 (i.e., the spatial lightmodulators 200). This configuration makes it possible to place theindividual spatial light modulators 5100 and the respectivelycorresponding SLM controller 5531, SLM controller 5532, and SLMcontroller 5533 close to each other, thereby enabling a high speed datatransfer rate.

Furthermore, a system bus 5580 is formed to connect to the frame memory5520, light source control unit 5560, sequencer 5540, and SLMcontrollers 5531 through 5533, in order to speed up and simplify theconnection path of each connecting element.

FIG. 31 is a functional block diagram for showing an exemplarymodification of a multi-panel projection apparatus according to anotherpreferred embodiment of the present invention.

The projection apparatus 5020 shown in FIG. 31 is implemented with twospatial light modulators 5100 (i.e., the spatial light modulators 200),each of which comprises the above described plate line 232, wherein onespatial light modulator 200 modulates the green light while the otherspatial light modulator 200 modulates the red and blue lights.

Specifically, projection apparatus 5020 comprises a dichroic mirror 5320as a light separation/synthesis optical system.

Dichroic mirror 5320 separates the wavelength component of a green lightand the wavelength components of red and blue lights from incidencelight 5601, which is incident from light source optical system 5200,causing them to branch into two spatial light modulators 200,respectively, synthesizing reflection light 5602 of the green lightreflected (i.e., modulated) by the corresponding spatial light modulator200 with the reflection light of the red and blue light reflected (i.e.,modulated) by the corresponding spatial light modulator 200 to guide thesynthesized light to the optical axis of projection optical system 5400,and projecting the synthesized light onto a screen 5900 as projectionlight 5603.

FIG. 32 is a block diagram for showing an example configuration of acontrol unit 5506 provided in projection apparatus 5020 comprising theabove-described two spatial light modulators 200. In this case, SLMcontroller 5530 controls two spatial light modulators 5100 (i.e., thespatial light modulators 200), which is the only difference from theconfiguration shown in FIG. 28.

FIG. 33 is a timing diagram for showing the waveform of a control signalof the projection apparatus according to the present embodiment.

A drive signal (i.e., a mirror control profile 450 shown in FIG. 33)generated by SLM controller 5530 drives multiple spatial lightmodulators 5100.

The light source control unit 5560 generates a light source profilecontrol signal 5800 corresponding to mirror control profile 450, whichis a signal for driving individual spatial light modulators 5100 forinputting the signal generated to light source drive circuit 5570, whichthen adjusts the intensity of the laser light (i.e., the illuminationlight 5600) emitted from the red laser light source 5211, the greenlaser light source 5212, and the blue laser light source 5213.

The control unit 5506 comprised in the projection apparatus 5020 isconfigured such that a single SLM controller 5530 drives the spatiallight modulators 5100, thereby enabling the irradiation of illuminationlight 5600 on the respective spatial light modulators 5100 with theoptimal quantity of light, without a requirement to configure the lightsource control unit 5560 or light source drive circuit 5570 for eachspatial light modulator 5100. This configuration simplifies the circuitconfiguration of the control unit 5506.

As shown in FIG. 33, the light source control unit 5560 and light sourcedrive circuit 5570 drives the red laser light source 5211, green laserlight source 5212, and blue laser light source 5213 so as to adjust theintensities of individual lasers (i.e., illumination light 5600) of thecolors R, G, and B synchronously with the irrespective SLM drive signals(i.e., the mirror control profile 450) generated by the SLM controller5530.

In this case, two colors, R and B, share one spatial light modulator5100, and therefore the control is a color sequential method.

That is, one frame includes multiple subfields, that include subfields6701, 6702, and 6703, and the same light source pulse pattern 6815 isrepeated in each subfield in one spatial light modulator 5100corresponding to green (G).

Meanwhile, the pulse emission of the red laser light source 5211 andblue laser light source 5213 for the red (R) and blue (B) lights thatshare one spatial light modulator 5100 are separately controlled.Therefore, the subfields that include subfields 6701 through 6703 arealternately applied in a time series as the light source pulse pattern6816 and light source pulse pattern 6817.

Furthermore, with the light source as described, the emission pulseintervals ti and emission pulse widths tp can be changed in the lightsource pulse pattern 6815 of the green laser, the light source pulsepattern 6816 of the red laser, and the light source pulse pattern 6817of the blue laser.

Therefore, the present embodiment can improve the levels of the grayscale for each of the R, G, and B colors.

According to above descriptions, the present invention discloses asystem configuration and method for increasing the definition of theprojection image while improving the levels of the gray scale for animage projection system implemented with a spatial light modulator.

Although the present invention has been described in terms of thepresently preferred embodiment, it is to be understood that suchdisclosure is not to be interpreted as limiting. Various alternationsand modifications will no doubt become apparent to those skilled in theart after reading the above disclosure. Accordingly, it is intended thatthe appended claims be interpreted as covering all alternations andmodifications as fall within the true spirit and scope of the invention.

1. A spatial light modulator, comprising: a pixel array comprises aplurality of pixel units; each of the pixel units further comprises amemory cell; a plurality of word lines and a plurality of plate linesfor electrically communicating with the pixel units; and a plurality ofbit line sets wherein each of the sets includes a pair of bit lines eachconnected to a memory cell, wherein at least one pair of the memorycells connected to the pair of bit lines are on a same row connected toa same word line.
 2. The spatial light modulator according to claim 1,wherein: at least two of the memory cells are connected to the set ofbit lines in one of the pixel units.
 3. The spatial light modulatoraccording to claim 1, wherein: every other of the memory cells on onerow in a direction along the word-line is connected to the bit line andplate line.
 4. The spatial light modulator according to claim 1,wherein: the memory cells connected to the bit line and the plate lineare configured at common relative location in each row in a directionalong the word line of the pixel array.
 5. The spatial light modulatoraccording to claim 1, further comprising: a bit driver for driving thesets of bit lines, wherein the bit driver has a first operation mode anda second operation mode, wherein a combinations of predetermined piecesof data set transmitted to the bit line set are different in the firstoperation mode and the second operation mode.
 6. The spatial lightmodulator according to claim 5, wherein: the data with a reversed logicstate is applied to each bit line of the bit line set in the firstoperation mode, and the data with the same logic state or reversed logicstate is applied to each bit line of the bit line set in the secondoperation.
 7. The spatial light modulator according to claim 5, wherein:the signal levels of the plate line are changed after the data of thesecond operation mode is applied by the bit line driver to the memorycell.
 8. The spatial light modulator according to claim 5, wherein: thesecond operation mode is carried out at least for one time during onesub-frame period for image display.
 9. The spatial light modulatoraccording to claim 1, wherein: each of the pixel units further comprisesa mirror.
 10. A spatial light modulator, comprising: a pixel arraycomprises a plurality of pixel units; each of the pixel units comprisesa memory cell for retaining data applied for driving the pixel unit; aplurality of word lines and a plurality of plate lines for electricallycommunicating with the pixel units; and a plurality of bit lines fortransmitting the data to the memory cell, wherein the memory comprises atransistor and a capacitor, a word line is connected to the gate of thetransistor, the first plate of the capacitor is connected to a source ofthe transistor to for connecting to the bit line, the second plate ofthe capacitor is connected to the plate line, a plurality of bit linesets wherein each of the sets includes two of the bit lines, and theplate line is connected to at least one of two of the memory cellsconnected to the set of bit lines wherein the memory cell are disposedon one row in a direction along the word line of the pixel array. 11.The spatial light modulator according to claim 1, wherein: each of thepixel units comprises a micromirror and an ON electrode and an OFFelectrode to control the micromirror to deflect to a range of tiltangles, the memory cells are electrically connected corresponding to anON electrode and an OFF electrode, the bit line is transmits a datasignal for storing in the memory cell, the word line controls thetransistor in each of the memory cells for controlling an operation ofwriting the data signal to the memory cell, and the plate line transmitsanother data signal to the memory cell
 12. The spatial light modulatoraccording to claim 10, wherein: each of the pixel units comprises amicromirror, and an ON electrode and an OFF electrode to control themicromirror to deflect within a range of tilt angles, the memory cellsare electrically connected correspondingly to an ON electrode and an OFFelectrode, the bit line is transmits a data signal for storing in thememory cell, the word line controls the transistor in each of the memorycells for controlling an operation of writing the data signal to thememory cell, and the plate line applies another data signal to thememory cell.